The Clinical Respiratory Journal
Diagnostic value of suPAR in differentiating noncardiac pleural effusions from cardiac pleural effusions Savas Ozsu1, Funda Oztuna1, Ahmet Mentese2, Yasin Abul1 and Tevfik Ozlu1 1 Pulmonary Medicine, Karadeniz Technical University Faculty of Medicine, Trabzon, Turkey 2 Department of Biochemistry, Karadeniz Technical University Faculty of Medicine, Trabzon, Turkey
Abstract Introduction: Soluble urokinase plasminogen activator receptor (suPAR) is a newly discovered inflammatory biomarker. suPAR has not been previously studied in differentiating noncardiac pleural effusion (PF) from cardiac PF. The aim of our study was to assess the diagnostic value of suPAR in PF. Methods: The concentration of PF-suPAR was measured by a commercialized enzyme-linked immunosorbent assay in a prospective cohort of 74 patients with PF, 18 patients with PF due to cardiac failure (CF) and 56 patients with noncardiac PF. The area under the curve quantified the overall diagnostic accuracy of the tests. Results: The median pleural fluid suPAR level was found as 23 (5.4–102.8) ng/mL. The median PF-suPAR level in CF was significantly lower than that of noncardiac effusions [11.8 (5.4–28.9) ng/mL vs 26.7 (8.2–102.8) ng/mL, respectively, P < 0.001]. The area under the receiver operating characteristic curve was 0.878 (95% confidence interval: 0795–0.962, P < 0.001) for noncardiac pleural fluid suPAR. The sensitivity, specificity and positive predictive value of PF-suPAR for noncardiac effusions at the cutoff level of ≥17.6 n/mL was 88%, 83% and 94%, respectively. The suPAR level in PF was found to correlate with all of the biochemical parameters of PF. Conclusions: suPAR is a potential new marker for the discrimination between cardiac and noncardiac PF.
Please Abul YY and Ozlu Ozlu T. T. Please cite cite this this paper as: Ozsu S, Oztuna F, Mentese A, Abul Diagnostic Diagnostic value value of suPAR in differentiating noncardiac pleural effusions from cardiac pleural pleuraleffusions. effusions.Clin ClinRespir RespirJ 2016; J 2014;10:••:61–66. ••–••. DOI:10.1111/crj.12186. cardiac DOI:10.1111/crj.12186.
Key words diagnosis – pleural effusion – soluble urokinase plasminogen activator receptor Correspondence Savas Ozsu, MD, Department of Chest Diseases, Karadeniz Technical University School of Medicine, Trabzon, Turkey Tel: +90 462 377 54 07 Fax: +90 462 325 70 31 email: [email protected]
Received: 25 December 2013 Revision requested: 02 June 2014 Accepted: 03 July 2014 DOI:10.1111/crj.12186 Authorship and contributorship Dr Ozsu contributed to the study concept and design, acquisition of data, analysis and interpretation of data, statistical analysis, critical revision of the manuscript for important intellectual content, and drafting of the manuscript. Dr Oztuna contributed to the study concept. Dr Mentese, biocehmical analysis, Dr Abul and Dr Ozlu contributed to the acquisition of data. Ethics The institutional ethics committee (Karadeniz Technical University, Faculty of Medicine, Trabzon, Turkey, No:2011/52) approved the study protocol, and a written informed consent was obtained from each participant at the time of sampling. Conflict of interest The authors have stated explicitly that there are no conflicts of interest in connection with this article.
Introduction Pleural effusions (PF) are commonly encountered in clinical practice and are caused by various mechanisms. In the assessment of the PF, the differentiation
(2014) • ISSN 1752-6981 The Clinical Respiratory Journal (2016) C 2014 V © 2014 John John Wiley Wiley && Sons Sons Ltd Ltd
between exudates and transudates should be made in the first place. The transudates occur due to serum ultrafiltration due to the increased hydrostatic pressure [cardiac failure (CF)] or decreased oncotic pressure (hypoalbuminemia). However, exudates mostly occur
suPAR in in pleural pleural effusions effusions suPAR
as a result of local inflammatory and infectious processes. CF is the underlying cause of most of the transudative effusions. However, up to 17%–39% of transudates are misdiagnosed as exudates, especially after receiving diuretic therapy and 5% the of malignant effusions may be misclassified as transudates (1, 2). On the other hand, exudative effusions are mainly parapneumonic (PPE), tuberculous and malignant effusions. Urokinase-type plasminogen activator receptor is expressed on neutrophils, lymphocytes, macrophages, endothelial and malignant cells. Soluble urokinase plasminogen activator receptor (suPAR) is a soluble form of the urokinase-type plasminogen activator receptor and it is a newly discovered inflammatory biomarker (3). suPAR has been tested as a prognostic and diagnostic tool in a number of infectious and inflammatory conditions. The elevated levels of suPAR in plasma correlate with poor clinical outcomes in patients suffering from cardiovascular diseases, from bacterial, viral and parasitic infectious diseases, as well as in patients with certain types of cancers (4). Of interest, suPAR is not only present in human plasma or serum, but also in pleural, pericardial and peritoneal fluids (5). However, the diagnostic role of suPAR in PF has not been previously investigated. The aim of this study was to determine the specific role of suPAR concentrations in the discrimination between noncardiac and cardiac PF.
Methods A total of selected 74 serum samples and pleural fluid samples obtained via thoracentesis were obtained prospectively and stored at 80°C. Patients with PF were enrolled in this study in a consecutive manner and classified into four groups: heart failure-related PF, PPEs, malignant pleural effusions (MPE) and miscellaneous exudative pleural effusions (mEPE). The fluid accumulations that were not related to heart failure were also classified as noncardiac PF.
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acteristics (6). In patients on diuretic therapy, the distinction between cardiac and noncardiac PF was made according to the albumin gradient. An albumin gradient higher than 1.2 suggested a transudate. The albumin gradient was calculated by subtracting the pleural albumin value from the serum albumin value. A diagnosis of PPE was based upon the presence of an effusion in patients with clinical and radiological evidence of acute pneumonia (i.e. patients with newly acquired respiratory symptoms, fever and abnormal breath sounds plus a new lung infiltrate seen on a chest radiograph). The diagnosis of heart failure (HF) was made according to clinical symptoms, including history, chest radiography, response to diuretic therapy and a left ventricular ejection fraction of ≤40% measured by echocardiography. All patients in the HF group were classified as stage III or IV in accordance with the New York Heart Association functional classification system. Pleural fluid was categorized as malignant if malignant cells were demonstrated in the fluid or pleural biopsy. A tuberculous pleural effusion (PE) was confirmed if the acid-fast bacilli was detected in the mycobacterial cultures of pleural fluid, sputum or the granulomatous inflammation was seen in the pleural biopsy specimen, or the latter showed granulomas in the parietal pleura or if exudative lymphocytes effusion with high adenosine deaminase levels (>40 IU/L) cleared in response to antituberculous therapy.
Biochemical analysis suPAR assay: levels of plasma suPAR were determined using an enzyme-linked immunosorbent assay kit (ViroGates A/S, Birkerød, Denmark, Product No: 203EK1-1) according to the manufacturer’s instructions. The absorbance of samples was measured at 450 nm using a VERSA max tunable microplate reader (designed by Molecular Devices, San Diego, CA, USA). The detection limit of the assay was estimated to be 0.1 ng/mL.
Statistical analysis Diagnostic criteria According to the Light’s criteria, any pleural fluid is considered as an exudate if any of the following criteria is met: the ratio of pleural fluid protein to serum protein is greater than 0.5, the ratio of pleural fluid lactate dehydrogenase (LDH) to serum LDH is greater than 0.6 and the pleural fluid LDH level is greater than the two thirds of the upper limits of the normal serum value. Transudative PF meet none of these three char62 2
Normal data distribution was investigated using the Kolmogorov–Smirnov test. Results are given as mean (standard deviation) or median (interquartile range), according to their distribution. Between-group comparisons of qualitative and quantitative variables were performed by using the Fisher exact test and Mann– Whitney U-test, respectively. One-way ANOVA was used for parametric variables and Kruskal–Wallis analysis for nonparametric variables. We assessed the
The Clinical Clinical Respiratory Respiratory Journal Journal (2014) (2016) •• ISSN ISSN 1752-6981 1752-6981 The C 2014 John Wiley & Sons Ltd V © 2014 John Wiley & Sons Ltd
suPAR effusions suPAR in in pleural pleural effusions
correlation between pleural fluid suPAR and other pleural parameters with the Spearman’s rank correlation. We constructed receiver operating characteristic (ROC) plots for suPAR and biochemical parameters and calculated the area under the curve for the comparison of the two diagnostic tests. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and likelihood ratios were calculated according to standard formulae. Light criteria and cut-off value of suPAR levels were first evaluated by univariate logistic regression analysis and then the parameters P < 0.10 included in multivariate logistic regression analysis (Table 4).
Soluble urokinase-type plasminogen activator activator receptor (suPAR)
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120,0 100,0 P < 0.001 80,0 60,0 40,0 20,0 0,0 Cardiac
Figure 1. Box-plots showing suPAR levels in pleural fluid in patients with cardiac and noncardiac effusions.
Results The study included 18 patients with PF due to CF, 56 patients noncardiac PF [22 cases of miscellaneous exudates tuberculous (n = 9), pulmonary embolism (n = 4), other (n = 8), 18 patients with PPE and 16 cases of malignancy], and as a result, 74 patients entered the study. The median age was 70 (18–99) years, and 44 (59.5%) of the overall cases were men. In our study, the median age of the patients with cardiac effusion was found higher than that of the patients with noncardiac effusion [79 (56–99) vs 65 (18–90) years, respectively P < 0.001)]. suPAR concentrations were measurable in all samples of PF. The median pleural fluid suPAR level was found as 23 (5.4–102.8) ng/mL. The median PF-suPAR level in CF was significantly lower than that of noncardiac effusions [11.8 (5.4–28.9) ng/mL vs 26.7 (8.2–102.8) ng/mL, respectively, P < 0.001] (Fig. 1). No significant difference was found among the suPAR levels of PPE, mEPE and malignant effusions (data not shown). The biochemical results of the PF of the patients were shown in Table 1.
A ROC analysis was used to identify the optimal PF-suPAR cut-off value for noncardiac PF. The area under the ROC curve was 0.878 [95% confidence interval (CI): 0795–0.962, P < 0.001] for pleural fluid suPAR (Fig. 2). The sensitivity, specificity and PPV of PF-suPAR for noncardiac effusions at the cut-off level of ≥17.6 n/mL was 88%, 83% and 94%, respectively. When compared with the other biochemical parameters, the suPAR level was determined as the best performing marker in the discrimination between cardiac and noncardiac PE (Table 2). When the suPAR level was below 17.6 ng/mL, the sensitivity, specificity, PPV and NPV were found 83%, 86%, 65% and 94% respectively. Three of the 18 (17%) patients with PF due to heart failure were misclassified as exudative PF according to Light’s criteria. The suPAR values of PF in these three patients were found