CLB-08869; No. of pages: 6; 4C: Clinical Biochemistry xxx (2014) xxx–xxx
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Usefulness of plasma neutrophil gelatinase-associated lipocalin as an early marker of acute kidney injury after cardiopulmonary bypass in Korean cardiac patients: A prospective observational study Chul Min Park a, Jun Seok Kim b, Hee-Won Moon d, Seungman Park c, Hanah Kim d, Misuk Ji d, Mina Hur d, Yeo-Min Yun d,⁎ a
Department of Laboratory Medicine, Dongnam Institute of Radiology and Medical Sciences, Busan, South Korea Department of Thoracic and Cardiovascular Surgery, Konkuk University School of Medicine, Seoul, South Korea c Department of Special Chemistry, Green Cross Laboratories, Gyeonggi, South Korea d Department of Laboratory Medicine, Konkuk University School of Medicine, Seoul, South Korea b
a r t i c l e
i n f o
Article history: Received 31 March 2014 Received in revised form 23 September 2014 Accepted 24 September 2014 Available online xxxx Keywords: Plasma NGAL Acute kidney injury Cardiopulmonary bypass Early biomarker
a b s t r a c t Objectives: Development of acute kidney injury (AKI) after cardiopulmonary bypass (CPB) is relatively common and associated with increased mortality. Recently, plasma neutrophil gelatinase-associated lipocalin (NGAL) was used for the prediction of AKI. We evaluated the clinical usefulness of plasma NGAL. Design and methods: One hundred twelve adult patients undergoing cardiovascular surgery with CPB were included. Blood samples were obtained at baseline, at intensive care unit (ICU) admission, and 24 h after ICU admission. The development of AKI, which is defined as an increase in serum creatinine by more than 50% within 3 postoperative days, was monitored. NGAL levels were analyzed by a Biosite Triage meter (Alere Medical, USA). Diagnostic performance of NGAL was analyzed using the area under the receiver operating characteristic curve. Results: In AKI patients (n = 13), plasma NGAL levels at ICU admission were significantly higher than those at baseline [177 (122–402) vs. 121 (74–158) ng/mL, median (interquartile range), p = 0.028], whereas serum creatinine showed no significant change. The predictive value of NGAL at ICU admission was 0.812 [95% confidence interval (CI), 0.68 to 0.95] with a cut-off value of 168.5 ng/mL (sensitivity, 61.5%; specificity, 88.9%). After the exclusion of 35 patients with preoperative decreased renal function, the predictive value was increased to 0.911 (95% CI, 0.82 to 1.00). Conclusions: This study showed that plasma NGAL may serve as a useful biomarker for the early detection of AKI in adult patients following CPB. © 2014 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.
Introduction Acute kidney injury (AKI) is a common complication occurring after cardiac surgery, affecting up to 50% of patients [1]. Once AKI occurs, it can have significant effects on the recipients, such as increased mortality, longer hospital stay, and greater resource utilization [2]. Although clinical risk factors associated with AKI after cardiac surgery have been well identified [2,3], accurate biomarkers for the Abbreviations: NGAL, neutrophil gelatinase-associated lipocalin; AKI, acute kidney injury; eGFR, estimated glomerular filtration rate; CPB, cardiopulmonary bypass; ICU, intensive care unit; POD, postoperative day; AuROC, area under the receiver operating characteristic curve; CI, confidence interval. ⁎ Corresponding author at: Department of Laboratory Medicine, Konkuk University School of Medicine, 120-1, Neungdong-ro, Gwangjin-gu, 143-729 Seoul, Korea. Fax: +82 2 2030 5587. E-mail address: [email protected] (Y.-M. Yun).
early identification of AKI are limited. Serum creatinine (Cr) is the most commonly used marker for monitoring renal function. But its levels may not increase until several days after renal tubular insult, thus causing delays in diagnosis and timely treatment of renal injury. Accordingly, there is a strong need for early and reliable markers for the monitoring of postoperative kidney dysfunction. Recently, neutrophil gelatinase-associated lipocalin (NGAL) was recognized as a strong candidate for an early marker of AKI. In previous studies, plasma and urine NGAL levels were considered good predictive markers in children and adult patients immediately after surgery [4–12]. Among these studies, only a small number included cardiac surgery patients, and a plasma NGAL cut-off value predictive of AKI was not clear in these patients [4,13]. We evaluated the clinical usefulness and appropriate cut-off value of plasma NGAL as an early biomarker for predicting postoperative AKI in patients undergoing cardiac surgery with cardiopulmonary bypass (CPB).
http://dx.doi.org/10.1016/j.clinbiochem.2014.09.019 0009-9120/© 2014 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.
Please cite this article as: Park CM, et al, Usefulness of plasma neutrophil gelatinase-associated lipocalin as an early marker of acute kidney injury after cardiopulmonary bypass ..., Clin Biochem (2014), http://dx.doi.org/10.1016/j.clinbiochem.2014.09.019
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Table 1 Characteristics of patients with or without AKI development after cardiopulmonary bypass surgery. Characteristic
Demographic data Age (years) Female (no.) Weight (kg) Body mass index (kg/m2) Comorbidities Diabetes (no.) Hypertension (no.) Repeat surgery (no.) Cardiopulmonary bypass pump time (hours) Preoperative laboratory data Serum creatinine (mg/dL) Serum BUN (mg/dL) eGFRc (mL/min/1.73 m2) eGFR b 60 mL/min/1.73 m2 (No.) Plasma NGAL (ng/mL)
Including 35 patients with preoperative renal impairment (n = 112)
Excluding patients with preoperative renal impairment (n = 77)
AKI (n = 13)
No AKI (n = 99)
p value
AKIn (n = 5)
No AKI (n = 72)
p value
65 (50, 74) 3 (23.1%) 64 (56, 76) 21.9 (20, 27.8)
54 (40, 61) 44 (44.4%) 64 (55, 70) 23 (21.3, 25)
0.022a 0.231b 0.810a 0.931a
41 (30, 59) 0 (0%) 80 (65, 91.5) 26.1 (19.8, 30.7)
48 (37, 58) 31 (43.1%) 64 (53.3, 70.8) 22.9 (21.1, 25)
0.726a 0.078b 0.024a 0.347a
2 (15.4%) 7 (53.8%) 4 (30.8%) 3.8 (2.8, 6.1)
6 (6.1%) 26 (26.3%) 15 (15.2%) 2.6 (2.0, 3.0)
0.233b 0.054b 0.230b 0.001a
1 (20.0%) 2 (40%) 3 (60%) 6.9 (3.6, 7.8)
3 (4.2%) 16 (22.2%) 12 (16.7%) 2.6 (2.1, 3.0)
0.240b 0.332b 0.048b b0.001a
0.98 (0.90, 1.16) 18.1 (16.2, 23.9) 55.0 (39.8, 72.3) 8 (61.5%)
0.85 (0.72, 0.98) 15.5 (13.7, 18.9) 69.4 (58.0, 78.2) 27 (27.3%)
0.020a 0.046a 0.054a 0.022b
0.87 (0.71, 0.92) 15.7 (12.6, 17.1) 74.8 (68.0, 107.4) –
0.78 (0.66, 0.87) 14.7 (12.8, 17.2) 74.7 (67.0, 82.1) –
0.450a 0.944a 0.487a –
121.0 (74.0, 157.5)
74.0 (54.0, 97.0)
0.007a
95.0 (64.0, 124.5)
62.5 (51.0, 84.8)
0.132 a
Values are presented as the median (interquartile range) or number (percentage). The p value was determined by the comparison between patients with or without AKI using the aMann–Whitney U or bFisher's exact test. c The eGFR, estimated glomerular filtration rate, was calculated using a revised equation for serum creatinine in Japan [16].
Materials and methods Subjects This study was approved by the institutional review board of the Konkuk University Medical Center (Seoul, Korea). Adult patients (over 18 years of age) undergoing cardiovascular surgery with CPB at the Konkuk University Medical Center were prospectively enrolled from March to October 2012. Patients with renal dysfunction who required routine dialysis and emergency surgery were excluded. Patients with simple procedures like isolated coronary artery bypass grafting or atrial septal defect repair were also excluded, due to the relatively low risk for postoperative AKI [14,15]. During the study period, 122 patients were initially enrolled. Five patients with insufficient samples for NGAL measurement and five patients without plasma NGAL data 24 h after intensive care unit (ICU) arrival were excluded. Demographic data of patients, information on comorbidities, and CPB pump time were obtained via electronic medical record review. Estimated glomerular filtration rate (eGFR) was calculated using a modified three-variable Japanese equation from serum Cr levels in Japan [16]. This new equation is based on a modification of diet in renal disease (MDRD) equation. Baseline eGFR greater than 60 mL/min/1.73 m2 was classified as normal renal function, and rates less than 60 mL/min/1.73 m2 as decreased renal function, according to the guideline of the National Kidney Foundation's Kidney Disease Outcomes Quality Initiative (NKF-KDOQI) [17]. Blood sample collection and analysis Plasma NGAL, serum creatinine (Cr), and serum urea levels were measured at baseline, at ICU admission, and 24 h after ICU admission. In addition, postoperative serum Cr was measured twice daily during a 3-day ICU stay to monitor the development of AKI. In most patients, sampling on admission to the ICU was done approximately 6 h after CPB surgery. After venous blood collection using EDTA and gel separator tubes (Greiner Bio-One, Austria), the samples were centrifuged at 2500–3000 rpm for 10 min within 1 h of collection, and the plasma or a serum fraction was used for measurement. The serum samples were stored at 4 °C for 2 h before assay. Serum Cr and urea were measured using commercially available reagent kits of the rate-blanked and compensated Jaffe method (Roche diagnostics, Germany) and enzymatic
method (Denka reagent, Japan), respectively, and a chemical analyzer (TBA-200FR NEO, Toshiba Medical Systems Co., Tokyo, Japan). Isotopedilution mass spectrometry traceable calibration was conducted daily for Cr measurements. Plasma NGAL was measured using the Triage NGAL point-of-care fluorescence immunoassay (Alere Inc., San Diego, CA) with a measureable range of 15–1300 ng/mL. EDTA plasma samples were analyzed within 12 h after sample collection, according to the manufacturer's recommendations. AKI definition Based on the RIFLE criteria of the Acute Dialysis Quality Initiative group [18], AKI was defined as an increase in serum Cr from baseline values by more than 50% within the first 3 postoperative days (PODs) after surgery. Considering the confounding effect of frequent diuretic use during the perioperative period, urine output criteria were excluded in the determination of AKI. Statistical analysis The Mann–Whitney U test and Wilcoxon rank sum test were used to compare independent and dependent (paired) continuous variables, respectively. For categorical variables, the Fisher's exact test was used. Areas under the receiver operating characteristic curve (AuROC) were analyzed to assess the diagnostic performance and optimal cut-off value of postoperative plasma NGAL to predict AKI. To assess the predictors of AKI development after CPB, univariate and multivariate logistic regression analyses were performed. Variables with univariate p values less than 0.1 (age, hypertension, CPB pump time, and renal biomarkers) were entered into the model for multivariate logistic regression analysis. Each renal biomarker was included one after the other (models 1–3) into the multivariate regression analysis to exclude interaction. PASW Statistics 17.0 (SPSS Inc., Chicago, IL, USA) and MedCalc Statistical software 13.3 (MedCalc Software bvba, Belgium) were used for statistical analysis. Results AKI development after adult cardiac surgery In Table 1, demographic and laboratory characteristics of patients with or without AKI development are shown for patients (n = 112)
Please cite this article as: Park CM, et al, Usefulness of plasma neutrophil gelatinase-associated lipocalin as an early marker of acute kidney injury after cardiopulmonary bypass ..., Clin Biochem (2014), http://dx.doi.org/10.1016/j.clinbiochem.2014.09.019
C.M. Park et al. / Clinical Biochemistry xxx (2014) xxx–xxx
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Fig. 1. Individual changes in serum Cr and plasma NGAL in patients with and without AKI at baseline, at the time of arrival to the intensive care unit (ICU), and 24 h after ICU admission for cardiopulmonary bypass surgery. Patients with an eGFR less than 60 mL/min/1.73 m2 were included. Values represent the median with parentheses indicating the interquartile range. p values were determined in patients with AKI using the Wilcoxon rank sum test. (A) Serum Cr in patients with AKI (n = 13); (B) serum Cr in patients without AKI (n = 99); (C) plasma NGAL in patients with AKI (n = 13); (D) plasma NGAL in patients without AKI (n = 99).
and patients without preoperative renal impairment (n = 77). Among 112 adult cardiac surgical patients, 13 patients (13/112, 11.6%) developed AKI after cardiac surgery with CPB. At the time of ICU admission after surgery, only one patient fulfilled the AKI diagnosis criterion based on increased serum Cr. The median detection time of 13 AKI patients by the Cr criterion was 22 h after surgery (range, from 2 to 46 h). The median age of the enrolled patients was 54 years (range, 21–78 years) and 65 (58%) patients were male. Among 112 subjects, 35 patients (35/112, 31.2%) had preoperative renal impairment with an eGFR less than 60 mL/min/1.73 m2. When these 35 patients were excluded, the incidence of AKI development after CPB significantly decreased [11.6% (13/112) vs. 6.5% (5/77), p = 0.022, Fisher's exact test]. Independent of preoperative renal impairment, patients who developed AKI had significantly longer CPB pump time than those without AKI. Plasma NGAL in AKI developed patients In Fig. 1, we present renal biomarkers in patients who developed AKI compared to those who did not develop AKI at baseline, on ICU admission, at 24 h after ICU admission. Data from the second analysis,
excluding patients with preoperative renal impairment (n = 35), are presented in Fig. 2. At baseline, renal biomarker concentrations were significantly higher in AKI patients compared to patients without AKI. However, when we exclude patients with preoperative renal impairment, renal biomarker concentrations were similar in patients, regardless of the development of AKI (Table 1). Not all AKI cases showed a marked rise in NGAL (Fig. 1C, Fig. 2C); however, plasma NGAL at postoperative ICU admission was significantly higher than that at baseline [177 (122–402) vs. 121 (74–158) ng/mL, median (interquartile range), p = 0.028, Wilcoxon rank sum test] in total, whereas serum Cr showed no significant change between baseline and ICU admission [1.02 (0.87–1.49) vs. 0.98 (0.90–1.16) mg/ dL, p = 0.906] (Fig. 1A and C). Independent of renal impairment, plasma NGAL at ICU admission was consistently higher than that at baseline, whereas serum Cr showed no significant change between baseline and ICU admission (Fig. 2A, Fig. 2C). Twenty-four hours after ICU admission, concentrations of serum Cr and plasma NGAL were significantly higher than those at baseline in the AKI group. Four out of 27 patients without AKI with low preoperative eGFR showed an increase in NGAL 24 h after ICU admission (Fig. 1D, Fig. 2D).
Please cite this article as: Park CM, et al, Usefulness of plasma neutrophil gelatinase-associated lipocalin as an early marker of acute kidney injury after cardiopulmonary bypass ..., Clin Biochem (2014), http://dx.doi.org/10.1016/j.clinbiochem.2014.09.019
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Fig. 2. Individual changes in serum Cr and plasma NGAL in patients with and without AKI at baseline, at the time of arrival to the intensive care unit (ICU), and 24 h after ICU admission for cardiopulmonary bypass surgery. Patients with an eGFR less than 60 mL/min/1.73 m2 were excluded. Values represent the median with parentheses indicating the interquartile range. p values were determined in patients with AKI using the Wilcoxon rank sum test. (A) Serum Cr in patients with AKI (n = 5); (B) serum Cr in patients without AKI (n = 72); (C) plasma NGAL in patients with AKI (n = 5); (D) plasma NGAL in patients without AKI (n = 72).
Plasma NGAL for AKI prediction The value of plasma NGAL to predict AKI is shown in Table 2. The AuROC of NGAL at ICU admission to predict AKI occurrence was 0.81 [95% confidence interval (CI), 0.68 to 0.95, p b 0.001]. At the time of ICU admission, a sensitivity of 61.5% and a specificity of 88.9% were observed for a plasma NGAL value of 168.5 ng/mL. After the exclusion of
patients with preoperative renal impairment, the power of plasma NGAL to predict AKI was increased (Table 2 and Fig. 3). Using multivariate logistic regression analysis, plasma NGAL (p = 0.015) and serum Cr (p = 0.036) levels were independent predictors of AKI development at ICU admission (Table 3). Other predictors of AKI were age and CPB pump time in model 0. Serum urea at ICU admission was not an independent predictor of AKI.
Table 2 Performance of plasma NGAL to predict AKI development after CPB surgery and effect of preoperative renal impairment. Factors
AuROC (95% CI)
Cut-off valueb (ng/mL)
Sensitivity
Specificity
p value
All subjects (n = 112) Subgroups divided by preoperative renal function eGFRa ≥ 60 (n = 77) eGFR b 60 (n = 35)
0.81 (0.68–0.95)
168.5
0.62
0.89
b0.001
0.91 (0.82–1.00) 0.68 (0.42–0.94)
168.5 –
0.80 –
0.89 –
0.002 0.135
AuROC, area under the receiver operating characteristic curve for the prediction of AKI; CI, confidence interval a eGFR (mL/min/1.73 m2), estimated glomerular filtration rate was calculated using a revised equation for serum Cr in Japan. b Cut-off values were obtained from the best threshold to maximize the sum of sensitivity and specificity in ROC analysis.
Please cite this article as: Park CM, et al, Usefulness of plasma neutrophil gelatinase-associated lipocalin as an early marker of acute kidney injury after cardiopulmonary bypass ..., Clin Biochem (2014), http://dx.doi.org/10.1016/j.clinbiochem.2014.09.019
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Fig. 3. Receiver operating characteristic (ROC) curve analysis for plasma NGAL. (A) In all subjects, including patients with preoperative renal impairment (eGFR b 60 mL/min/ 1.73 m2), the AuROC is 0.812 (95% CI, 0.68–0.95) to predict the development of AKI after CPB surgery. (B) When excluding patients with preoperative renal impairment (eGFR b 60 mL/min/1.73 m2), the power of plasma NGAL to predict AKI development increased (AuROC, 0.911; 95% CI, 0.82–1.00).
Discussion In this study, we have shown that after cardiac surgery, the rate of increase of plasma NGAL was higher than serum Cr, suggesting the usefulness of plasma NGAL as an early biomarker of AKI (Figs. 1 and 2). At the time of ICU admission, plasma NGAL increased significantly in patients who developed AKI, whereas serum Cr levels did not increase. Serum Cr was not significantly elevated until POD 1. We confirmed that an early postoperative increase in plasma NGAL is a better marker for the prediction of AKI than is serum Cr. The incidence of AKI after CPB in this study (13/117, 11.1%) was significantly lower than that in
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published research [15,19]. Hobson et al. reported the incidence of AKI to be greater than 50%, and Che et al. reported an incidence of AKI of 31% in the Chinese population. Differences in AKI incidence could be caused by distinct study subjects' constitutions (underlying disease, operation type, age/sex distribution) and/or the skills of treatment practices during the hospital stay. Additionally, the diagnostic value of plasma NGAL to predict AKI varied according to baseline renal function (Table 2). After the exclusion of patients with preoperative renal impairment (eGFR b 60 mL/min/1.73 m2), the predictive value of plasma NGAL was increased [0.911 (95% CI, 0.82–1.00)]. The performance of plasma NGAL was superior in patients with normal renal function. Based on previous studies, plasma or urinary NGAL is considered as an early biomarker of kidney damage. The usefulness of NGAL as a marker of renal damage has been evaluated in studies of cardiac surgery patients, as well as kidney transplant, contrast nephropathy, and ICU patients. In 2005, Mishra et al. first reported the usefulness of plasma and urinary NGAL for predicting AKI after pediatric cardiac surgery [4], and Koyner et al. reported that urinary NGAL could be useful for predicting AKI in adult cardiac patients in 2008 [9]. Some clinical models were evaluated for the purpose of AKI prediction after cardiac surgery [20]. Because there were little data for estimating such a clinical model in Korean population, we adopted the clinical model from Parikh et al. [21] with some modifications. Their clinical models included common variables in other AKI models, such as age, sex, race, CPB time, nonelective surgery, preoperative eGFR, diabetes, and hypertension. Considering the specific conditions of our study group, we excluded some variables like race and emergency operation from the multivariate analysis. Tuladhar et al. [11] reported that plasma NGAL had an AuROC of 0.85 to predict AKI after adult cardiac surgery. In another study, the AuROC was 0.73 [12]. These results are similar to ours, as we report an AuROC of 0.812–0.911. AuROC analysis suggested that a plasma NGAL cut-off value of 72 ng/mL at ICU admission had 100% sensitivity for AKI development after CPB. Given a rather poor positive predictive value of 15.1%, a plasma NGAL value of 72 ng/mL or greater probably does not serve as a good biomarker for predicting AKI development in this study population. On the contrary, cut-off values greater than 430 ng/mL show 100% specificity but 21.1% sensitivity. Unlike most previous studies that used stored, frozen plasma, we measured NGAL with fresh EDTA-preserved whole blood. The plasma and urine NGAL values are known to be stable when stored at − 80 °C, but there are reports of decreased stability when stored at − 20 °C [22–24]. NGAL values in this study are supposed to have no bias caused by long-term storage, since they were measured in the same manner as actual practices. For the estimation of GFR, we selected a revised Japanese MDRD equation (modified three-variable Japanese equation) for serum Cr levels [16]. According to the NKF-KDOQI, the MDRD and Cockcroft– Gault equations are recommended for eGFR calculations. The MDRD equation has been widely used, but estimations using this equation have limited accuracy, especially in the elderly and in patients with normal serum Cr. Also, the original MDRD equation is known to be less accurate in Asian patients, especially when the eGFR is less than 60 mL/min/1.73 m2 [16]. Accordingly, we used the new Japanese equation due to similar ethnicities. However, there are several limitations of our study. First, we used estimated GFR values for the determination of preoperative renal function instead of GFR measurements. Second, a GFR of 60 mL/min/1.73 m2 was considered to be the universal criterion without adjusting for agedependent reference intervals. Additionally, the number of AKI cases was relatively low; thus, there might be some bias for direct comparisons between patients with and without AKI. Among patients with normal renal function, one case with AKI showed very high NGAL levels (Fig. 2C), which may possibly confound the overall mean. However, AKI incidence could depend upon many factors, as previously mentioned, and this study may represent one variable clinical situation. Lastly, we could not validate the cut-off value of postoperative plasma NGAL
Please cite this article as: Park CM, et al, Usefulness of plasma neutrophil gelatinase-associated lipocalin as an early marker of acute kidney injury after cardiopulmonary bypass ..., Clin Biochem (2014), http://dx.doi.org/10.1016/j.clinbiochem.2014.09.019
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Table 3 Multivariate logistic regression analysis of risk factors to predict AKI development after CPB surgery. Model 0 (R2 = 0.457)
Age (years) Hypertension CPB pump time (hours) Plasma NGAL at ICU admission (ng/mL) Serum Cr at ICU admission (mg/dL) Serum urea at ICU admission (mg/dL)
Model 1 (R2 = 0.549)
Regression coefficient (B) (SE)
p
Regression coefficient (B) (SE)
0.063 (0.030) 1.291 (0.827) 1.257 (0.336)
0.036 0.041 (0.032) 0.119 1.510 (0.942) 0.001 1.218 (0.378) 0.010 (0.004)
Model 2 (R2 = 0.526) p
Regression coefficient (B) (SE)
0.205 0.045 (0.032) 0.109 0.781 (0.950) 0.001 1.215 (0.362)
Model 3 (R2 = 0.491) p
Regression coefficient (B) (SE)
0.157 0.043 (0.032) 0.411 1.043 (0.891) 0.001 1.203 (0.349)
p 0.177 0.242 0.001
0.015 3.065 (1.463)
0.036 0.114 (0.073)
0.119
SE, standard error; ICU, intensive care unit. Each renal biomarker (plasma NGAL, serum Cr, and serum urea) was included, one after the other (models 1–3) in the multivariate regression analysis to exclude interactions. Multivariate logistic regression analysis included variables with univariate p values less than 0.1 (age, hypertension, CPB pump time, and renal biomarkers).
levels to predict AKI prospectively in an independent cohort. Further studies are thus needed for confirmation. In conclusion, this study supports the use of plasma NGAL as a useful biomarker for the early detection of AKI in adult patients following CPB. Our study suggests a preliminary cut-off value of 168.5 ng/mL in CPB patients with normal renal function and other populations, although this value must be validated in prospective studies. Acknowledgments This paper was written as part of Konkuk University's research support program in 2011. References [1] Bove T, Calabro MG, Landoni G, Aletti G, Marino G, Crescenzi G, et al. The incidence and risk of acute renal failure after cardiac surgery. J Cardiothorac Vasc Anesth 2004; 18:442–5. [2] Chertow GM, Burdick E, Honour M, Bonventre JV, Bates DW. Acute kidney injury, mortality, length of stay, and costs in hospitalized patients. J Am Soc Nephrol 2005;16:3365–70. [3] Thakar CV, Worley S, Arrigain S, Yared JP, Paganini EP. Influence of renal dysfunction on mortality after cardiac surgery: modifying effect of preoperative renal function. Kidney Int 2005;67:1112–9. [4] Mishra J, Dent C, Tarabishi R, Mitsnefes MM, Ma Q, Kelly C, et al. Neutrophil gelatinase-associated lipocalin (ngal) as a biomarker for acute renal injury after cardiac surgery. Lancet 2005;365:1231–8. [5] Wagener G, Jan M, Kim M, Mori K, Barasch JM, Sladen RN, et al. Association between increases in urinary neutrophil gelatinase-associated lipocalin and acute renal dysfunction after adult cardiac surgery. Anesthesiology 2006;105:485–91. [6] Dent CL, Ma Q, Dastrala S, Bennett M, Mitsnefes MM, Barasch J, et al. Plasma neutrophil gelatinase-associated lipocalin predicts acute kidney injury, morbidity and mortality after pediatric cardiac surgery: a prospective uncontrolled cohort study. Crit Care 2007;11:R127. [7] Wagener G, Gubitosa G, Wang S, Borregaard N, Kim M, Lee HT. Urinary neutrophil gelatinase-associated lipocalin and acute kidney injury after cardiac surgery. Am J Kidney Dis 2008;52:425–33. [8] Bennett M, Dent CL, Ma Q, Dastrala S, Grenier F, Workman R, et al. Urine NGAL predicts severity of acute kidney injury after cardiac surgery: a prospective study. Clin J Am Soc Nephrol 2008;3:665–73. [9] Koyner JL, Bennett MR, Worcester EM, Ma Q, Raman J, Jeevanandam V, et al. Urinary cystatin C as an early biomarker of acute kidney injury following adult cardiothoracic surgery. Kidney Int 2008;74:1059–69.
[10] Xin C, Yulong X, Yu C, Changchun C, Feng Z, Xinwei M. Urine neutrophil gelatinaseassociated lipocalin and interleukin-18 predict acute kidney injury after cardiac surgery. Ren Fail 2008;30:904–13. [11] Tuladhar SM, Puntmann VO, Soni M, Punjabi PP, Bogle RG. Rapid detection of acute kidney injury by plasma and urinary neutrophil gelatinase-associated lipocalin after cardiopulmonary bypass. J Cardiovasc Pharmacol 2009;53:261–6. [12] Haase-Fielitz A, Bellomo R, Devarajan P, Story D, Matalanis G, Dragun D, et al. Novel and conventional serum biomarkers predicting acute kidney injury in adult cardiac surgery—a prospective cohort study. Crit Care Med 2009;37:553–60. [13] Haase M, Bellomo R, Devarajan P, Schlattmann P, Haase-Fielitz A. Accuracy of neutrophil gelatinase-associated lipocalin (NGAL) in diagnosis and prognosis in acute kidney injury: a systematic review and meta-analysis. Am J Kidney Dis 2009;54: 1012–24. [14] Wijeysundera DN, Karkouti K, Dupuis JY, Rao V, Chan CT, Granton JT, et al. Derivation and validation of a simplified predictive index for renal replacement therapy after cardiac surgery. JAMA 2007;297:1801–9. [15] Hobson CE, Yavas S, Segal MS, Schold JD, Tribble CG, Layon AJ, et al. Acute kidney injury is associated with increased long-term mortality after cardiothoracic surgery. Circulation 2009;119:2444–53. [16] Matsuo S, Imai E, Horio M, Yasuda Y, Tomita K, Nitta K, et al. Revised equations for estimated GFR from serum creatinine in Japan. Am J Kidney Dis 2009;53:982–92. [17] K/DOQI clinical practice guidelines for chronic kidney disease: evaluation, classification, and stratification. Am J Kidney Dis 2002;39:S1–S266. [18] Bellomo R, Ronco C, Kellum JA, Mehta RL, Palevsky P. Acute renal failure — definition, outcome measures, animal models, fluid therapy and information technology needs: the second international consensus conference of the acute dialysis quality initiative (ADQI) group. Crit Care 2004;8:R204–12. [19] Che M, Li Y, Liang X, Xie B, Xue S, Qian J, et al. Prevalence of acute kidney injury following cardiac surgery and related risk factors in Chinese patients. Nephron Clin Pract 2011;117:c305–11. [20] Kiers HD, van den Boogaard M, Schoenmakers MC, van der Hoeven JG, van Swieten HA, Heemskerk S, et al. Comparison and clinical suitability of eight prediction models for cardiac surgery-related acute kidney injury. Nephrol Dial Transplant 2013;28:345–51. [21] Parikh CR, Devarajan P, Zappitelli M, Sint K, Thiessen-Philbrook H, Li S, et al. Postoperative biomarkers predict acute kidney injury and poor outcomes after pediatric cardiac surgery. J Am Soc Nephrol 2011;22:1737–47. [22] Haase-Fielitz A, Haase M, Bellomo R. Instability of urinary NGAL during long-term storage. Am J Kidney Dis 2009;53:564–5 [author reply 6]. [23] Grenier FC, Ali S, Syed H, Workman R, Martens F, Liao M, et al. Evaluation of the architect urine NGAL assay: assay performance, specimen handling requirements and biological variability. Clin Biochem 2010;43:615–20. [24] Pedersen KR, Ravn HB, Hjortdal VE, Norregaard R, Povlsen JV. Neutrophil gelatinaseassociated lipocalin (NGAL): validation of commercially available elisa. Scand J Clin Lab Invest 2010;70:374–82.
Please cite this article as: Park CM, et al, Usefulness of plasma neutrophil gelatinase-associated lipocalin as an early marker of acute kidney injury after cardiopulmonary bypass ..., Clin Biochem (2014), http://dx.doi.org/10.1016/j.clinbiochem.2014.09.019
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Usefulness of plasma neutrophil gelatinase-associated lipocalin as an early marker of acute kidney injury after cardiopulmonary bypass in Korean cardiac patients: A prospective observational study Chul Min Park a, Jun Seok Kim b, Hee-Won Moon d, Seungman Park c, Hanah Kim d, Misuk Ji d, Mina Hur d, Yeo-Min Yun d,⁎ a
Department of Laboratory Medicine, Dongnam Institute of Radiology and Medical Sciences, Busan, South Korea Department of Thoracic and Cardiovascular Surgery, Konkuk University School of Medicine, Seoul, South Korea c Department of Special Chemistry, Green Cross Laboratories, Gyeonggi, South Korea d Department of Laboratory Medicine, Konkuk University School of Medicine, Seoul, South Korea b
a r t i c l e
i n f o
Article history: Received 31 March 2014 Received in revised form 23 September 2014 Accepted 24 September 2014 Available online xxxx Keywords: Plasma NGAL Acute kidney injury Cardiopulmonary bypass Early biomarker
a b s t r a c t Objectives: Development of acute kidney injury (AKI) after cardiopulmonary bypass (CPB) is relatively common and associated with increased mortality. Recently, plasma neutrophil gelatinase-associated lipocalin (NGAL) was used for the prediction of AKI. We evaluated the clinical usefulness of plasma NGAL. Design and methods: One hundred twelve adult patients undergoing cardiovascular surgery with CPB were included. Blood samples were obtained at baseline, at intensive care unit (ICU) admission, and 24 h after ICU admission. The development of AKI, which is defined as an increase in serum creatinine by more than 50% within 3 postoperative days, was monitored. NGAL levels were analyzed by a Biosite Triage meter (Alere Medical, USA). Diagnostic performance of NGAL was analyzed using the area under the receiver operating characteristic curve. Results: In AKI patients (n = 13), plasma NGAL levels at ICU admission were significantly higher than those at baseline [177 (122–402) vs. 121 (74–158) ng/mL, median (interquartile range), p = 0.028], whereas serum creatinine showed no significant change. The predictive value of NGAL at ICU admission was 0.812 [95% confidence interval (CI), 0.68 to 0.95] with a cut-off value of 168.5 ng/mL (sensitivity, 61.5%; specificity, 88.9%). After the exclusion of 35 patients with preoperative decreased renal function, the predictive value was increased to 0.911 (95% CI, 0.82 to 1.00). Conclusions: This study showed that plasma NGAL may serve as a useful biomarker for the early detection of AKI in adult patients following CPB. © 2014 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.
Introduction Acute kidney injury (AKI) is a common complication occurring after cardiac surgery, affecting up to 50% of patients [1]. Once AKI occurs, it can have significant effects on the recipients, such as increased mortality, longer hospital stay, and greater resource utilization [2]. Although clinical risk factors associated with AKI after cardiac surgery have been well identified [2,3], accurate biomarkers for the Abbreviations: NGAL, neutrophil gelatinase-associated lipocalin; AKI, acute kidney injury; eGFR, estimated glomerular filtration rate; CPB, cardiopulmonary bypass; ICU, intensive care unit; POD, postoperative day; AuROC, area under the receiver operating characteristic curve; CI, confidence interval. ⁎ Corresponding author at: Department of Laboratory Medicine, Konkuk University School of Medicine, 120-1, Neungdong-ro, Gwangjin-gu, 143-729 Seoul, Korea. Fax: +82 2 2030 5587. E-mail address: [email protected] (Y.-M. Yun).
early identification of AKI are limited. Serum creatinine (Cr) is the most commonly used marker for monitoring renal function. But its levels may not increase until several days after renal tubular insult, thus causing delays in diagnosis and timely treatment of renal injury. Accordingly, there is a strong need for early and reliable markers for the monitoring of postoperative kidney dysfunction. Recently, neutrophil gelatinase-associated lipocalin (NGAL) was recognized as a strong candidate for an early marker of AKI. In previous studies, plasma and urine NGAL levels were considered good predictive markers in children and adult patients immediately after surgery [4–12]. Among these studies, only a small number included cardiac surgery patients, and a plasma NGAL cut-off value predictive of AKI was not clear in these patients [4,13]. We evaluated the clinical usefulness and appropriate cut-off value of plasma NGAL as an early biomarker for predicting postoperative AKI in patients undergoing cardiac surgery with cardiopulmonary bypass (CPB).
http://dx.doi.org/10.1016/j.clinbiochem.2014.09.019 0009-9120/© 2014 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.
Please cite this article as: Park CM, et al, Usefulness of plasma neutrophil gelatinase-associated lipocalin as an early marker of acute kidney injury after cardiopulmonary bypass ..., Clin Biochem (2014), http://dx.doi.org/10.1016/j.clinbiochem.2014.09.019
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C.M. Park et al. / Clinical Biochemistry xxx (2014) xxx–xxx
Table 1 Characteristics of patients with or without AKI development after cardiopulmonary bypass surgery. Characteristic
Demographic data Age (years) Female (no.) Weight (kg) Body mass index (kg/m2) Comorbidities Diabetes (no.) Hypertension (no.) Repeat surgery (no.) Cardiopulmonary bypass pump time (hours) Preoperative laboratory data Serum creatinine (mg/dL) Serum BUN (mg/dL) eGFRc (mL/min/1.73 m2) eGFR b 60 mL/min/1.73 m2 (No.) Plasma NGAL (ng/mL)
Including 35 patients with preoperative renal impairment (n = 112)
Excluding patients with preoperative renal impairment (n = 77)
AKI (n = 13)
No AKI (n = 99)
p value
AKIn (n = 5)
No AKI (n = 72)
p value
65 (50, 74) 3 (23.1%) 64 (56, 76) 21.9 (20, 27.8)
54 (40, 61) 44 (44.4%) 64 (55, 70) 23 (21.3, 25)
0.022a 0.231b 0.810a 0.931a
41 (30, 59) 0 (0%) 80 (65, 91.5) 26.1 (19.8, 30.7)
48 (37, 58) 31 (43.1%) 64 (53.3, 70.8) 22.9 (21.1, 25)
0.726a 0.078b 0.024a 0.347a
2 (15.4%) 7 (53.8%) 4 (30.8%) 3.8 (2.8, 6.1)
6 (6.1%) 26 (26.3%) 15 (15.2%) 2.6 (2.0, 3.0)
0.233b 0.054b 0.230b 0.001a
1 (20.0%) 2 (40%) 3 (60%) 6.9 (3.6, 7.8)
3 (4.2%) 16 (22.2%) 12 (16.7%) 2.6 (2.1, 3.0)
0.240b 0.332b 0.048b b0.001a
0.98 (0.90, 1.16) 18.1 (16.2, 23.9) 55.0 (39.8, 72.3) 8 (61.5%)
0.85 (0.72, 0.98) 15.5 (13.7, 18.9) 69.4 (58.0, 78.2) 27 (27.3%)
0.020a 0.046a 0.054a 0.022b
0.87 (0.71, 0.92) 15.7 (12.6, 17.1) 74.8 (68.0, 107.4) –
0.78 (0.66, 0.87) 14.7 (12.8, 17.2) 74.7 (67.0, 82.1) –
0.450a 0.944a 0.487a –
121.0 (74.0, 157.5)
74.0 (54.0, 97.0)
0.007a
95.0 (64.0, 124.5)
62.5 (51.0, 84.8)
0.132 a
Values are presented as the median (interquartile range) or number (percentage). The p value was determined by the comparison between patients with or without AKI using the aMann–Whitney U or bFisher's exact test. c The eGFR, estimated glomerular filtration rate, was calculated using a revised equation for serum creatinine in Japan [16].
Materials and methods Subjects This study was approved by the institutional review board of the Konkuk University Medical Center (Seoul, Korea). Adult patients (over 18 years of age) undergoing cardiovascular surgery with CPB at the Konkuk University Medical Center were prospectively enrolled from March to October 2012. Patients with renal dysfunction who required routine dialysis and emergency surgery were excluded. Patients with simple procedures like isolated coronary artery bypass grafting or atrial septal defect repair were also excluded, due to the relatively low risk for postoperative AKI [14,15]. During the study period, 122 patients were initially enrolled. Five patients with insufficient samples for NGAL measurement and five patients without plasma NGAL data 24 h after intensive care unit (ICU) arrival were excluded. Demographic data of patients, information on comorbidities, and CPB pump time were obtained via electronic medical record review. Estimated glomerular filtration rate (eGFR) was calculated using a modified three-variable Japanese equation from serum Cr levels in Japan [16]. This new equation is based on a modification of diet in renal disease (MDRD) equation. Baseline eGFR greater than 60 mL/min/1.73 m2 was classified as normal renal function, and rates less than 60 mL/min/1.73 m2 as decreased renal function, according to the guideline of the National Kidney Foundation's Kidney Disease Outcomes Quality Initiative (NKF-KDOQI) [17]. Blood sample collection and analysis Plasma NGAL, serum creatinine (Cr), and serum urea levels were measured at baseline, at ICU admission, and 24 h after ICU admission. In addition, postoperative serum Cr was measured twice daily during a 3-day ICU stay to monitor the development of AKI. In most patients, sampling on admission to the ICU was done approximately 6 h after CPB surgery. After venous blood collection using EDTA and gel separator tubes (Greiner Bio-One, Austria), the samples were centrifuged at 2500–3000 rpm for 10 min within 1 h of collection, and the plasma or a serum fraction was used for measurement. The serum samples were stored at 4 °C for 2 h before assay. Serum Cr and urea were measured using commercially available reagent kits of the rate-blanked and compensated Jaffe method (Roche diagnostics, Germany) and enzymatic
method (Denka reagent, Japan), respectively, and a chemical analyzer (TBA-200FR NEO, Toshiba Medical Systems Co., Tokyo, Japan). Isotopedilution mass spectrometry traceable calibration was conducted daily for Cr measurements. Plasma NGAL was measured using the Triage NGAL point-of-care fluorescence immunoassay (Alere Inc., San Diego, CA) with a measureable range of 15–1300 ng/mL. EDTA plasma samples were analyzed within 12 h after sample collection, according to the manufacturer's recommendations. AKI definition Based on the RIFLE criteria of the Acute Dialysis Quality Initiative group [18], AKI was defined as an increase in serum Cr from baseline values by more than 50% within the first 3 postoperative days (PODs) after surgery. Considering the confounding effect of frequent diuretic use during the perioperative period, urine output criteria were excluded in the determination of AKI. Statistical analysis The Mann–Whitney U test and Wilcoxon rank sum test were used to compare independent and dependent (paired) continuous variables, respectively. For categorical variables, the Fisher's exact test was used. Areas under the receiver operating characteristic curve (AuROC) were analyzed to assess the diagnostic performance and optimal cut-off value of postoperative plasma NGAL to predict AKI. To assess the predictors of AKI development after CPB, univariate and multivariate logistic regression analyses were performed. Variables with univariate p values less than 0.1 (age, hypertension, CPB pump time, and renal biomarkers) were entered into the model for multivariate logistic regression analysis. Each renal biomarker was included one after the other (models 1–3) into the multivariate regression analysis to exclude interaction. PASW Statistics 17.0 (SPSS Inc., Chicago, IL, USA) and MedCalc Statistical software 13.3 (MedCalc Software bvba, Belgium) were used for statistical analysis. Results AKI development after adult cardiac surgery In Table 1, demographic and laboratory characteristics of patients with or without AKI development are shown for patients (n = 112)
Please cite this article as: Park CM, et al, Usefulness of plasma neutrophil gelatinase-associated lipocalin as an early marker of acute kidney injury after cardiopulmonary bypass ..., Clin Biochem (2014), http://dx.doi.org/10.1016/j.clinbiochem.2014.09.019
C.M. Park et al. / Clinical Biochemistry xxx (2014) xxx–xxx
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Fig. 1. Individual changes in serum Cr and plasma NGAL in patients with and without AKI at baseline, at the time of arrival to the intensive care unit (ICU), and 24 h after ICU admission for cardiopulmonary bypass surgery. Patients with an eGFR less than 60 mL/min/1.73 m2 were included. Values represent the median with parentheses indicating the interquartile range. p values were determined in patients with AKI using the Wilcoxon rank sum test. (A) Serum Cr in patients with AKI (n = 13); (B) serum Cr in patients without AKI (n = 99); (C) plasma NGAL in patients with AKI (n = 13); (D) plasma NGAL in patients without AKI (n = 99).
and patients without preoperative renal impairment (n = 77). Among 112 adult cardiac surgical patients, 13 patients (13/112, 11.6%) developed AKI after cardiac surgery with CPB. At the time of ICU admission after surgery, only one patient fulfilled the AKI diagnosis criterion based on increased serum Cr. The median detection time of 13 AKI patients by the Cr criterion was 22 h after surgery (range, from 2 to 46 h). The median age of the enrolled patients was 54 years (range, 21–78 years) and 65 (58%) patients were male. Among 112 subjects, 35 patients (35/112, 31.2%) had preoperative renal impairment with an eGFR less than 60 mL/min/1.73 m2. When these 35 patients were excluded, the incidence of AKI development after CPB significantly decreased [11.6% (13/112) vs. 6.5% (5/77), p = 0.022, Fisher's exact test]. Independent of preoperative renal impairment, patients who developed AKI had significantly longer CPB pump time than those without AKI. Plasma NGAL in AKI developed patients In Fig. 1, we present renal biomarkers in patients who developed AKI compared to those who did not develop AKI at baseline, on ICU admission, at 24 h after ICU admission. Data from the second analysis,
excluding patients with preoperative renal impairment (n = 35), are presented in Fig. 2. At baseline, renal biomarker concentrations were significantly higher in AKI patients compared to patients without AKI. However, when we exclude patients with preoperative renal impairment, renal biomarker concentrations were similar in patients, regardless of the development of AKI (Table 1). Not all AKI cases showed a marked rise in NGAL (Fig. 1C, Fig. 2C); however, plasma NGAL at postoperative ICU admission was significantly higher than that at baseline [177 (122–402) vs. 121 (74–158) ng/mL, median (interquartile range), p = 0.028, Wilcoxon rank sum test] in total, whereas serum Cr showed no significant change between baseline and ICU admission [1.02 (0.87–1.49) vs. 0.98 (0.90–1.16) mg/ dL, p = 0.906] (Fig. 1A and C). Independent of renal impairment, plasma NGAL at ICU admission was consistently higher than that at baseline, whereas serum Cr showed no significant change between baseline and ICU admission (Fig. 2A, Fig. 2C). Twenty-four hours after ICU admission, concentrations of serum Cr and plasma NGAL were significantly higher than those at baseline in the AKI group. Four out of 27 patients without AKI with low preoperative eGFR showed an increase in NGAL 24 h after ICU admission (Fig. 1D, Fig. 2D).
Please cite this article as: Park CM, et al, Usefulness of plasma neutrophil gelatinase-associated lipocalin as an early marker of acute kidney injury after cardiopulmonary bypass ..., Clin Biochem (2014), http://dx.doi.org/10.1016/j.clinbiochem.2014.09.019
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Fig. 2. Individual changes in serum Cr and plasma NGAL in patients with and without AKI at baseline, at the time of arrival to the intensive care unit (ICU), and 24 h after ICU admission for cardiopulmonary bypass surgery. Patients with an eGFR less than 60 mL/min/1.73 m2 were excluded. Values represent the median with parentheses indicating the interquartile range. p values were determined in patients with AKI using the Wilcoxon rank sum test. (A) Serum Cr in patients with AKI (n = 5); (B) serum Cr in patients without AKI (n = 72); (C) plasma NGAL in patients with AKI (n = 5); (D) plasma NGAL in patients without AKI (n = 72).
Plasma NGAL for AKI prediction The value of plasma NGAL to predict AKI is shown in Table 2. The AuROC of NGAL at ICU admission to predict AKI occurrence was 0.81 [95% confidence interval (CI), 0.68 to 0.95, p b 0.001]. At the time of ICU admission, a sensitivity of 61.5% and a specificity of 88.9% were observed for a plasma NGAL value of 168.5 ng/mL. After the exclusion of
patients with preoperative renal impairment, the power of plasma NGAL to predict AKI was increased (Table 2 and Fig. 3). Using multivariate logistic regression analysis, plasma NGAL (p = 0.015) and serum Cr (p = 0.036) levels were independent predictors of AKI development at ICU admission (Table 3). Other predictors of AKI were age and CPB pump time in model 0. Serum urea at ICU admission was not an independent predictor of AKI.
Table 2 Performance of plasma NGAL to predict AKI development after CPB surgery and effect of preoperative renal impairment. Factors
AuROC (95% CI)
Cut-off valueb (ng/mL)
Sensitivity
Specificity
p value
All subjects (n = 112) Subgroups divided by preoperative renal function eGFRa ≥ 60 (n = 77) eGFR b 60 (n = 35)
0.81 (0.68–0.95)
168.5
0.62
0.89
b0.001
0.91 (0.82–1.00) 0.68 (0.42–0.94)
168.5 –
0.80 –
0.89 –
0.002 0.135
AuROC, area under the receiver operating characteristic curve for the prediction of AKI; CI, confidence interval a eGFR (mL/min/1.73 m2), estimated glomerular filtration rate was calculated using a revised equation for serum Cr in Japan. b Cut-off values were obtained from the best threshold to maximize the sum of sensitivity and specificity in ROC analysis.
Please cite this article as: Park CM, et al, Usefulness of plasma neutrophil gelatinase-associated lipocalin as an early marker of acute kidney injury after cardiopulmonary bypass ..., Clin Biochem (2014), http://dx.doi.org/10.1016/j.clinbiochem.2014.09.019
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Fig. 3. Receiver operating characteristic (ROC) curve analysis for plasma NGAL. (A) In all subjects, including patients with preoperative renal impairment (eGFR b 60 mL/min/ 1.73 m2), the AuROC is 0.812 (95% CI, 0.68–0.95) to predict the development of AKI after CPB surgery. (B) When excluding patients with preoperative renal impairment (eGFR b 60 mL/min/1.73 m2), the power of plasma NGAL to predict AKI development increased (AuROC, 0.911; 95% CI, 0.82–1.00).
Discussion In this study, we have shown that after cardiac surgery, the rate of increase of plasma NGAL was higher than serum Cr, suggesting the usefulness of plasma NGAL as an early biomarker of AKI (Figs. 1 and 2). At the time of ICU admission, plasma NGAL increased significantly in patients who developed AKI, whereas serum Cr levels did not increase. Serum Cr was not significantly elevated until POD 1. We confirmed that an early postoperative increase in plasma NGAL is a better marker for the prediction of AKI than is serum Cr. The incidence of AKI after CPB in this study (13/117, 11.1%) was significantly lower than that in
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published research [15,19]. Hobson et al. reported the incidence of AKI to be greater than 50%, and Che et al. reported an incidence of AKI of 31% in the Chinese population. Differences in AKI incidence could be caused by distinct study subjects' constitutions (underlying disease, operation type, age/sex distribution) and/or the skills of treatment practices during the hospital stay. Additionally, the diagnostic value of plasma NGAL to predict AKI varied according to baseline renal function (Table 2). After the exclusion of patients with preoperative renal impairment (eGFR b 60 mL/min/1.73 m2), the predictive value of plasma NGAL was increased [0.911 (95% CI, 0.82–1.00)]. The performance of plasma NGAL was superior in patients with normal renal function. Based on previous studies, plasma or urinary NGAL is considered as an early biomarker of kidney damage. The usefulness of NGAL as a marker of renal damage has been evaluated in studies of cardiac surgery patients, as well as kidney transplant, contrast nephropathy, and ICU patients. In 2005, Mishra et al. first reported the usefulness of plasma and urinary NGAL for predicting AKI after pediatric cardiac surgery [4], and Koyner et al. reported that urinary NGAL could be useful for predicting AKI in adult cardiac patients in 2008 [9]. Some clinical models were evaluated for the purpose of AKI prediction after cardiac surgery [20]. Because there were little data for estimating such a clinical model in Korean population, we adopted the clinical model from Parikh et al. [21] with some modifications. Their clinical models included common variables in other AKI models, such as age, sex, race, CPB time, nonelective surgery, preoperative eGFR, diabetes, and hypertension. Considering the specific conditions of our study group, we excluded some variables like race and emergency operation from the multivariate analysis. Tuladhar et al. [11] reported that plasma NGAL had an AuROC of 0.85 to predict AKI after adult cardiac surgery. In another study, the AuROC was 0.73 [12]. These results are similar to ours, as we report an AuROC of 0.812–0.911. AuROC analysis suggested that a plasma NGAL cut-off value of 72 ng/mL at ICU admission had 100% sensitivity for AKI development after CPB. Given a rather poor positive predictive value of 15.1%, a plasma NGAL value of 72 ng/mL or greater probably does not serve as a good biomarker for predicting AKI development in this study population. On the contrary, cut-off values greater than 430 ng/mL show 100% specificity but 21.1% sensitivity. Unlike most previous studies that used stored, frozen plasma, we measured NGAL with fresh EDTA-preserved whole blood. The plasma and urine NGAL values are known to be stable when stored at − 80 °C, but there are reports of decreased stability when stored at − 20 °C [22–24]. NGAL values in this study are supposed to have no bias caused by long-term storage, since they were measured in the same manner as actual practices. For the estimation of GFR, we selected a revised Japanese MDRD equation (modified three-variable Japanese equation) for serum Cr levels [16]. According to the NKF-KDOQI, the MDRD and Cockcroft– Gault equations are recommended for eGFR calculations. The MDRD equation has been widely used, but estimations using this equation have limited accuracy, especially in the elderly and in patients with normal serum Cr. Also, the original MDRD equation is known to be less accurate in Asian patients, especially when the eGFR is less than 60 mL/min/1.73 m2 [16]. Accordingly, we used the new Japanese equation due to similar ethnicities. However, there are several limitations of our study. First, we used estimated GFR values for the determination of preoperative renal function instead of GFR measurements. Second, a GFR of 60 mL/min/1.73 m2 was considered to be the universal criterion without adjusting for agedependent reference intervals. Additionally, the number of AKI cases was relatively low; thus, there might be some bias for direct comparisons between patients with and without AKI. Among patients with normal renal function, one case with AKI showed very high NGAL levels (Fig. 2C), which may possibly confound the overall mean. However, AKI incidence could depend upon many factors, as previously mentioned, and this study may represent one variable clinical situation. Lastly, we could not validate the cut-off value of postoperative plasma NGAL
Please cite this article as: Park CM, et al, Usefulness of plasma neutrophil gelatinase-associated lipocalin as an early marker of acute kidney injury after cardiopulmonary bypass ..., Clin Biochem (2014), http://dx.doi.org/10.1016/j.clinbiochem.2014.09.019
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Table 3 Multivariate logistic regression analysis of risk factors to predict AKI development after CPB surgery. Model 0 (R2 = 0.457)
Age (years) Hypertension CPB pump time (hours) Plasma NGAL at ICU admission (ng/mL) Serum Cr at ICU admission (mg/dL) Serum urea at ICU admission (mg/dL)
Model 1 (R2 = 0.549)
Regression coefficient (B) (SE)
p
Regression coefficient (B) (SE)
0.063 (0.030) 1.291 (0.827) 1.257 (0.336)
0.036 0.041 (0.032) 0.119 1.510 (0.942) 0.001 1.218 (0.378) 0.010 (0.004)
Model 2 (R2 = 0.526) p
Regression coefficient (B) (SE)
0.205 0.045 (0.032) 0.109 0.781 (0.950) 0.001 1.215 (0.362)
Model 3 (R2 = 0.491) p
Regression coefficient (B) (SE)
0.157 0.043 (0.032) 0.411 1.043 (0.891) 0.001 1.203 (0.349)
p 0.177 0.242 0.001
0.015 3.065 (1.463)
0.036 0.114 (0.073)
0.119
SE, standard error; ICU, intensive care unit. Each renal biomarker (plasma NGAL, serum Cr, and serum urea) was included, one after the other (models 1–3) in the multivariate regression analysis to exclude interactions. Multivariate logistic regression analysis included variables with univariate p values less than 0.1 (age, hypertension, CPB pump time, and renal biomarkers).
levels to predict AKI prospectively in an independent cohort. Further studies are thus needed for confirmation. In conclusion, this study supports the use of plasma NGAL as a useful biomarker for the early detection of AKI in adult patients following CPB. Our study suggests a preliminary cut-off value of 168.5 ng/mL in CPB patients with normal renal function and other populations, although this value must be validated in prospective studies. Acknowledgments This paper was written as part of Konkuk University's research support program in 2011. References [1] Bove T, Calabro MG, Landoni G, Aletti G, Marino G, Crescenzi G, et al. The incidence and risk of acute renal failure after cardiac surgery. J Cardiothorac Vasc Anesth 2004; 18:442–5. [2] Chertow GM, Burdick E, Honour M, Bonventre JV, Bates DW. Acute kidney injury, mortality, length of stay, and costs in hospitalized patients. J Am Soc Nephrol 2005;16:3365–70. [3] Thakar CV, Worley S, Arrigain S, Yared JP, Paganini EP. Influence of renal dysfunction on mortality after cardiac surgery: modifying effect of preoperative renal function. Kidney Int 2005;67:1112–9. [4] Mishra J, Dent C, Tarabishi R, Mitsnefes MM, Ma Q, Kelly C, et al. Neutrophil gelatinase-associated lipocalin (ngal) as a biomarker for acute renal injury after cardiac surgery. Lancet 2005;365:1231–8. [5] Wagener G, Jan M, Kim M, Mori K, Barasch JM, Sladen RN, et al. Association between increases in urinary neutrophil gelatinase-associated lipocalin and acute renal dysfunction after adult cardiac surgery. Anesthesiology 2006;105:485–91. [6] Dent CL, Ma Q, Dastrala S, Bennett M, Mitsnefes MM, Barasch J, et al. Plasma neutrophil gelatinase-associated lipocalin predicts acute kidney injury, morbidity and mortality after pediatric cardiac surgery: a prospective uncontrolled cohort study. Crit Care 2007;11:R127. [7] Wagener G, Gubitosa G, Wang S, Borregaard N, Kim M, Lee HT. Urinary neutrophil gelatinase-associated lipocalin and acute kidney injury after cardiac surgery. Am J Kidney Dis 2008;52:425–33. [8] Bennett M, Dent CL, Ma Q, Dastrala S, Grenier F, Workman R, et al. Urine NGAL predicts severity of acute kidney injury after cardiac surgery: a prospective study. Clin J Am Soc Nephrol 2008;3:665–73. [9] Koyner JL, Bennett MR, Worcester EM, Ma Q, Raman J, Jeevanandam V, et al. Urinary cystatin C as an early biomarker of acute kidney injury following adult cardiothoracic surgery. Kidney Int 2008;74:1059–69.
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Please cite this article as: Park CM, et al, Usefulness of plasma neutrophil gelatinase-associated lipocalin as an early marker of acute kidney injury after cardiopulmonary bypass ..., Clin Biochem (2014), http://dx.doi.org/10.1016/j.clinbiochem.2014.09.019
