Scandinavian Journal of Clinical & Laboratory Investigation, 2014; Early Online: 1–4
ORIGINAL ARTICLE
Cutoff values for bacteria and leukocytes for urine sediment analyzer FUS200 in culture-positive urinary-tract infections
Scand J Clin Lab Invest Downloaded from informahealthcare.com by University of Southern California on 04/09/14 For personal use only.
DERYA KOCER1, FATMA M. SARİGUZEL2 & CİGDEM KARAKUKCU1 1Department
of Clinical Biochemistry, and 2Department of Microbiology, Training and Research Hospital, Kayseri,
Turkey Abstract Objectives. The microscopic analysis of urine is essential for the diagnosis of patients with urinary tract infections. Quantitative urine culture is the ‘gold standard’ method for definitive diagnosis of urinary-tract infections, but it is laborintensive, time consuming, and does not provide the same-day results. The aim of this study was to evaluate the analytical and diagnostic performance of the FUS200 (Changchun Dirui Industry, China), a new urine sedimentation analyzer in comparison to urine culture as the reference method. Methods. We evaluated 1000 urine samples, submitted for culture and urine analysis with a preliminary diagnosis of urinary-tract infection. Cut-off values for the FUS200 were determined by comparing the results with urine cultures. The cut-off values by the receiver operating characteristic (ROC) curve technique, sensitivity, and specificity were calculated for bacteria and white blood cells (WBCs). Results. Among the 1000 urine specimens submitted for culture, 637 cultures (63.7%) were negative, and 363 were (36.3%) positive. The best cut-off values obtained from ROC analysis were 16/μL for bacteriuria (sensitivity: 82.3%, specificity: 58%), and 34/μL for WBCs (sensitivity: 72.3%, specificity: 65.2%). The area under the curve (AUC) for the bacteria and WBCs count were 0.71 (95% CI: 0.67–0.74) and, 0.72 (95% CI: 0.69–0.76) respectively. Conclusions. The most important requirement of a rapid diagnostic screening test is sensitivity, and, in this perspective, an unsatisfactory sensitivity by using bacteria recognition and quantification performed by the FUS200 analyzer has been observed. After further technical improvements in particle recognition and laboratory personnel training, the FUS200 might show better results. Key Words: FUS200, urinalysis, analytic performance, urine culture
Introduction The microscopic analysis of urine is essential for the diagnosis and monitoring of patients with urinarytract infections [1]. The automation of this test has been developed over the last few years. Quantitative urine culture and identification are still the ‘gold standard’ laboratory procedures for definitive diagnosis of urinary-tract infections, but it is laborintensive, time consuming, and does not provide the same-day results [2,3]. Furthermore, often it is unnecessarily applied to negative samples. By an effective screening test unnecessary culture can be reduced [4]. The FUS200/H800 is a new instrument which has the measurement principles based on the Flowing Microscopy Imaging System. The instrument is capable of detecting and counting urinary particles
sedimented by sheath flow technique. With the two layers of sheath outside, the sample enters the system after being aspirated. Under the effect of a double layer sheath, the urine sample enters the cell flow in the form of single cell layer. Images are captured at a high speed. The sheath is isosmotic and stable with no particle. The sheath, which has buffer and preservation function, can inhibit bacterial growth in urine and can ensure the visible component in urine is always at the focus of the microscope lens. Each particle at the lens is seen with its largest area when passing through in accordance with sheath flow principle. When each view of the microscope is illuminated by high-speed flashing light source (40 times per second), all passing visible component can be captured. Within a certain time, the FUS200 CCD camera captures 650 frames of
Correspondence: Derya Kocer, Department of Biochemistry, Kayseri Training and Research Hospital, 38030 Kayseri, Turkey. Tel: ⴙ 90 352 336 88 84. Fax: ⫹ 90 352 320 73 13. E-mail: [email protected] (Received 3 December 2013 ; accepted 20 February 2014 ) ISSN 0036-5513 print/ISSN 1502-7686 online © 2014 Informa Healthcare DOI: 10.3109/00365513.2014.900189
2
D. Kocer et al.
images containing visible component for each sample. All images are evaluated by a high quality image processing software which is able to detect and classify the urine particles. The aim of this study was to evaluate the analytical and diagnostic performance of FUS200 (Changchun Dirui Industry, China), a new urine sedimentation analyzer in comparison to urine culture as the reference method which has not been investigated yet.
Chicago, Illinois, USA). To determine the best cutoff values, the receiver operating characteristic (ROC) curve technique for bacteria and white blood cells (WBCs) were performed. Positive predictive value (PPV), negative predictive value (NPV) and accuracy rate at the best cut-off values for bacteria and WBCs were also calculated considering the urine culture as the reference. A value of p ⬍ 0.05 was considered as statistically significant.
Scand J Clin Lab Invest Downloaded from informahealthcare.com by University of Southern California on 04/09/14 For personal use only.
Results Materials and methods We retrospectively evaluated 1000 urine samples, submitted for culture and urine analysis to the Clinical Microbiology and Clinical Biochemistry Laboratories in Training and Research Hospital, Kayseri, Turkey, between June 2012 and December 2012. All urine samples were from outpatients to exclude hospital acquired infections. Specimens from inpatients or outpatients who had been hospitalized within the previous month were excluded. Spot midstream urine samples (10 mL, n ⫽ 1000) collected in accordance with standard guidelines (detailed instructions for collection were provided) using a disposable, sterile, neutral container, screw lid (Firatmed® Sterile Urine Sampling Container) were randomly selected for the study. In newborn and infants, sterile urine collection bags were used. All urine samples were collected on the morning of the examination, processed within 2 hours after collection and within 30 minutes after their submission to the laboratory. Automated urine analysis and quantitative culture were applied to all specimens. Urine particles were detected and classified by FUS200, and the FUS200-assigned classifications were edited by laboratory technicians. WBC and bacteria were counted per high-power field (hpf, 400 ⫻ magnification). Counts in hpf correspond to particle/μL ⫻ 6.25. Samples were cultured by application of 10 μL urine on 5% blood agar and eosine methylene blue agar plates (Oxoid, UK). Cultures were incubated at 37°C for 24 hours. Bacterial counts were expressed as the number of colony-forming units (CFUs) per milliliter. Growth of ⬍ 104 CFUs/mL was considered negative, which is the standard for diagnosis in pediatric patients and patients admitted to the intensive care unit in our hospital. If there were three or more kinds of colonies without a dominant species, the urine was considered contaminated. The Vitek®II system (BioMérieux, Marcy l’Etoile, France) was used for identification of microorganisms.
Of 1000 specimens, 760 were female with a mean age of 28.7 years (range 0–83 years) and 240 were male with a mean age 31.0 years (range 0–84 years) who belonged to the following general groups: pediatrics (n ⫽ 451), nephrology (n ⫽ 248), family medicine (n ⫽ 88), internal medicine (n ⫽ 51), urology (n ⫽ 47), infectious diseases (n ⫽ 30), physical therapy and rehabilitation (n ⫽ 28), pediatric nephrology (n ⫽ 17), cardiology (n ⫽ 14), and others (n ⫽ 26). The samples from infants aged between 0 and 3 years and children aged between 4 and 16 years accounted for 7.7% and 38.1% of the total number of samples, respectively. Among the 1000 urine specimens submitted for culture, 637 cultures (63.7%) were negative, while significant microbiological growth was detected in 363 specimens (36.3%). Organisms isolated from 363 positive urine cultures and their numbers of cases are shown in Table I. As expected, Escherichia coli was found to be the most common pathogen (70%) in this study. Growth of three or more different colonies was considered as contaminated (n ⫽ 9, 0.9%) and excluded from the study. Unexpectedly, we detected that, of 363 positive urine cultures, 82 samples showed no bacteria in the automated urine analysis. The ROC curves for bacteria and WBCs counts are shown in Figure 1, in which culture results ⱖ 104 CFB/L were taken as the reference for significant bacteriuria. The area under the curve (AUC) for the bacteria and WBCs count were 0.71 (95% CI: 0.67–0.74) and, 0.72 (95% CI: 0.69–0.76) respectively. There was no significant difference between AUCs of bacteria and WBCs count (p ⫽ 0.308). The best cut-off values obtained from the ROC analysis were 16/μL for bacteriuria (sensitivity: 82.3%, specificity: 58%), and 34/μL for WBCs (sensitivity: 72.3%, specificity: 65.2%). PPV, NPV and accuracy rate at the best cut-off values for bacteria and WBCs were also determined, and the results are shown in Table II.
Statistical Analysis
Discussion
Statistical analysis was carried out by SPSS® 15.0 (Statistical Packages for Social Sciences; SPSS Inc,
The FUS200 is a new automated urine sediment analyzer for identification and counting of bright-field
Analytical performance of FUS200 Table I. Organisms isolated from 363 positive urine cultures.
Scand J Clin Lab Invest Downloaded from informahealthcare.com by University of Southern California on 04/09/14 For personal use only.
Microorganism Escherichia coli Klebsiella pneumonia Proteus spp. Staphylococcus coagulase negative Enterococcus faecalis Staphylococcus aureus Staphylococcus epidermidis Streptococcus agalactiae Pseudomonas aeruginosa Morganella morganii Streptococcus haemolyticus Citrobacter brakii Candida spp. Maya Citrobacter freundii Acinetobacter baumannii Kontaminasyon Total
Number of cases 255 25 18 14 8 8 6 4 5 3 3 1 1 1 1 1 9 363
digital images of the formed elements in urine. It can be connected to a urine strip chemistry analyzer to provide an integrated chemical and microscopic urinalysis workstation. In this retrospective study we evaluated the performance of the FUS200 in comparison with the urine culture method for screening urine samples for urinary system infections. In the present study, we used only urine specimens from outpatients. Since the specimens from patients who have been hospitalized have characteristics different from those of patients with community-acquired urinary-tract infections, due to antibiotics, catheters and etc. [5,6], these samples were excluded. The best cut-off point found in our study by comparing culture and bacterial count with the
Figure 1. Receiver operating characteristic curves for bacteria and WBCs cut-off values.
3
Table II. Analytical performance of FUS200 at the best cut-off values for bacterial and WBCs count in 1000 specimens with cases positive in culture (versus urine quantitative culture).
Sensitivity (%) Specificity (%) Positive Predictive Value (%) Negative Predictive Value (%) Accuracy Rate (%)
Bacterial count Cut-off 16/μL
WBCs count Cut-off 34/μL
82.3 58.0 65.0 77.5 73.5
72.3 65.2 57.1 78.5 69.7
FUS200 was 16 bacteria/μL (Table II). This value is significantly lower than the data reported on previous studies for different automated urine sediment analyzers. To the best of our knowledge, analytic performance of the FUS200 has not so far been researched. Earlier studies which have shown cut-off values have demonstrated ranges between 125–170 bacteria/μL for UF-1000i [3,7,8], 1000–6000 bacteria/μL for UF-100 [2,9–11] and 85 bacteria/μL for UriSed. During the data collection for this study, we detected that 82 urine samples with positive cultures had no bacteria in the automated urine analysis. This may lead to consideration of bacteria identification and quantification problem of the FUS200. An optimal screening method must ensure primarily a high sensitivity and a NPV in ruling out the diagnosis of a urinary-tract infection. The European Urinalysis Guidelines recommend an analytical sensitivity ⬎ 90–95% to detect bacteriuria at 105 CFU/mL by a rapid non-culture method with a confirmatory culture of positive cases [12]. At a cut-off value of 16 bacteria/μL, the sensitivity was 82.3%, NPV 77.5%, and the percentage of samples that did not need to be cultured was 65%. These sensitivity and NPV values are lower than the recommendation of The European Urinalysis Guidelines. We also evaluated the sensitivity, specificity, PPV, and NPV for WBCs because the presence of leukocytes is crucial in urinary system-infection diagnosis and the evaluation of the success of treatment [13]. The best cut-off value obtained by ROC analysis was 34 WBCs/μL with the sensitivity of 72.3% and NPV of 78.5%. This result was similar to the data reported in previous studies for different automated urine sediment analyzers [2,9–11,14]. As shown by the ROC curve analysis in this study (Figure 1), diagnostic values of bacteria and leukocytes were similar (AUC: 0.710 and 0.728 respectively, p ⫽ 0.308). Since the cut-off values of bacteria and WBC counts may change due to the patient population, the type of specimens and the selected threshold for significant counts in culture, each laboratory must examine and report these values [3]. Also, because different automated systems report
Scand J Clin Lab Invest Downloaded from informahealthcare.com by University of Southern California on 04/09/14 For personal use only.
4
D. Kocer et al.
different cut-off values for bacteria and WBC counts due to the analyzing method, physicians should know the system used in their laboratory for urine analysis and assess the results with respect to the cut-off values of their own analyzer used. In the present study, the main purpose of screening urine specimens was to find out if it is possible to predict positive cultures and thereby eliminate the negative cultures rapidly and safely. The most important requirement of a rapid diagnostic screening test is sensitivity, and, in this perspective, an unsatisfactory sensitivity by using bacteria recognition and quantification performed by the FUS200 analyzer has been observed. According to the manufacturer, the FUS200 is able to detect and classify erythrocytes, leukocytes and squamous epithelial cells. However, for other elements in urine it is recommended to review images on-screen by trained laboratory personnel to make a definitive diagnosis. So this problem may also be related to ineffective identification by laboratory technicians. After further technical improvements in particle recognition and laboratory personnel training, the FUS200 might show better results.
Acknowledgements None to declare.
Declaration of interest: The authors have no conflicts of interest. The authors alone are responsible for the content and writing of the paper. References [1] Fogazzi GB, Ponticelli C, Ritz E. The urinary sediment in the main diseases of the urinary tract. In: Fogazzi GB, Ponticelli C, Ritz E, editors. The urinary sediment: an integrated view. 2nd edn. Oxford: Oxford University Press; 1999. pp. 139–60.
[2] Zaman Z, Roggeman S, Verhaegen J. Unsatisfactory performance of flow cytometer UF-100 and urine strips in predicting outcome of urine cultures. J Clin Microbiol 2001;39:4169–71. [3] De Rosa R, Grosso S, Bruschetta G, Avolio M, Stano P, Modolo ML, Camporese A. Evaluation of the Sysmex UF1000i flow cytometer for ruling out bacterial urinary tract infection. Clinica Chimica Acta 2010;411:1137–42. [4] Karakukcu C, Kayman T, Ozturk A, Torun YA. Analytic performance of bacteriuria and leukocyturia obtained by UriSed in culture positive urinary tract infections. Clin Lab 2012;58:107–11. [5] Foxman B. Epidemiology of urinary tract infections: incidence, morbidity, and economic costs. Am J Med 2002; 113(Suppl. 1A):5S–13S. [6] Jones RN. Impact of changing pathogens and antimicrobial susceptibility patterns in the treatment of serious infections in hospitalized patients. Am J Med 1996; 100:3S–12S. [7] Manoni F, Fornasiero L, Ercolin M, Tinello A, Ferrian M, Hoffer P, Valverde S, Gessoni G. Cutoff values for bacteria and leukocytes for urine flow cytometer Sysmex UF-1000i in urinary tract infections. Diagn Microbiol Infect Dis 2009; 65:103–7. [8] Wang J, Zhang Y, Xu D, Shao W, Lu Y. Evaluation of the Sysmex UF-1000i for the diagnosis of urinary tract infection. Am J Clin Pathol 2010;133:577–82. [9] Evans R, Davidson M, Sim L, Hay A. Testing by Sysmex UF-100 flow cytometer and with bacterial culture in a diagnostic laboratory – a comparison. J Clin Pathol 2006; 59:661–2. [10] Koken T, Aktepe O, Serteser M, Samli M, Kahraman A, Dogan N. Determination of cut-off values for leukocytes and bacteria for urine flow cytometer (UF-100) in urinary tract infection. Int Urol Nephrol 2002;34:175–8. [11] Manoni F, Valverde S, Antico F, Salvadego M, Giacomini A, Gessoni G. Field evaluation of a second generation cytometer UF-100 in diagnosis of acute urinary tract infections in adult patients. Clin Microbiol Infect 2002;8:662–8. [12] European Confederation of Laboratory Medicine. European urinalysis guidelines. Scand J Clin Lab Invest 2000; 231(Suppl.):1–86. [13] Ottiger C, Schaer G, Huber AR. Time-course of quantitative urinary leukocyte bacteria counts during antibiotic therapy in women with symptoms of urinary tract infection. Clin Chim Acta 2007;379:36–41. [14] Kayalp D, Dogan K, Ceylan G, Senes M, Yucel D. Can routine automated urinalysis reduce culture requests? Clin Biochem 2013;46:1285–9.
ORIGINAL ARTICLE
Cutoff values for bacteria and leukocytes for urine sediment analyzer FUS200 in culture-positive urinary-tract infections
Scand J Clin Lab Invest Downloaded from informahealthcare.com by University of Southern California on 04/09/14 For personal use only.
DERYA KOCER1, FATMA M. SARİGUZEL2 & CİGDEM KARAKUKCU1 1Department
of Clinical Biochemistry, and 2Department of Microbiology, Training and Research Hospital, Kayseri,
Turkey Abstract Objectives. The microscopic analysis of urine is essential for the diagnosis of patients with urinary tract infections. Quantitative urine culture is the ‘gold standard’ method for definitive diagnosis of urinary-tract infections, but it is laborintensive, time consuming, and does not provide the same-day results. The aim of this study was to evaluate the analytical and diagnostic performance of the FUS200 (Changchun Dirui Industry, China), a new urine sedimentation analyzer in comparison to urine culture as the reference method. Methods. We evaluated 1000 urine samples, submitted for culture and urine analysis with a preliminary diagnosis of urinary-tract infection. Cut-off values for the FUS200 were determined by comparing the results with urine cultures. The cut-off values by the receiver operating characteristic (ROC) curve technique, sensitivity, and specificity were calculated for bacteria and white blood cells (WBCs). Results. Among the 1000 urine specimens submitted for culture, 637 cultures (63.7%) were negative, and 363 were (36.3%) positive. The best cut-off values obtained from ROC analysis were 16/μL for bacteriuria (sensitivity: 82.3%, specificity: 58%), and 34/μL for WBCs (sensitivity: 72.3%, specificity: 65.2%). The area under the curve (AUC) for the bacteria and WBCs count were 0.71 (95% CI: 0.67–0.74) and, 0.72 (95% CI: 0.69–0.76) respectively. Conclusions. The most important requirement of a rapid diagnostic screening test is sensitivity, and, in this perspective, an unsatisfactory sensitivity by using bacteria recognition and quantification performed by the FUS200 analyzer has been observed. After further technical improvements in particle recognition and laboratory personnel training, the FUS200 might show better results. Key Words: FUS200, urinalysis, analytic performance, urine culture
Introduction The microscopic analysis of urine is essential for the diagnosis and monitoring of patients with urinarytract infections [1]. The automation of this test has been developed over the last few years. Quantitative urine culture and identification are still the ‘gold standard’ laboratory procedures for definitive diagnosis of urinary-tract infections, but it is laborintensive, time consuming, and does not provide the same-day results [2,3]. Furthermore, often it is unnecessarily applied to negative samples. By an effective screening test unnecessary culture can be reduced [4]. The FUS200/H800 is a new instrument which has the measurement principles based on the Flowing Microscopy Imaging System. The instrument is capable of detecting and counting urinary particles
sedimented by sheath flow technique. With the two layers of sheath outside, the sample enters the system after being aspirated. Under the effect of a double layer sheath, the urine sample enters the cell flow in the form of single cell layer. Images are captured at a high speed. The sheath is isosmotic and stable with no particle. The sheath, which has buffer and preservation function, can inhibit bacterial growth in urine and can ensure the visible component in urine is always at the focus of the microscope lens. Each particle at the lens is seen with its largest area when passing through in accordance with sheath flow principle. When each view of the microscope is illuminated by high-speed flashing light source (40 times per second), all passing visible component can be captured. Within a certain time, the FUS200 CCD camera captures 650 frames of
Correspondence: Derya Kocer, Department of Biochemistry, Kayseri Training and Research Hospital, 38030 Kayseri, Turkey. Tel: ⴙ 90 352 336 88 84. Fax: ⫹ 90 352 320 73 13. E-mail: [email protected] (Received 3 December 2013 ; accepted 20 February 2014 ) ISSN 0036-5513 print/ISSN 1502-7686 online © 2014 Informa Healthcare DOI: 10.3109/00365513.2014.900189
2
D. Kocer et al.
images containing visible component for each sample. All images are evaluated by a high quality image processing software which is able to detect and classify the urine particles. The aim of this study was to evaluate the analytical and diagnostic performance of FUS200 (Changchun Dirui Industry, China), a new urine sedimentation analyzer in comparison to urine culture as the reference method which has not been investigated yet.
Chicago, Illinois, USA). To determine the best cutoff values, the receiver operating characteristic (ROC) curve technique for bacteria and white blood cells (WBCs) were performed. Positive predictive value (PPV), negative predictive value (NPV) and accuracy rate at the best cut-off values for bacteria and WBCs were also calculated considering the urine culture as the reference. A value of p ⬍ 0.05 was considered as statistically significant.
Scand J Clin Lab Invest Downloaded from informahealthcare.com by University of Southern California on 04/09/14 For personal use only.
Results Materials and methods We retrospectively evaluated 1000 urine samples, submitted for culture and urine analysis to the Clinical Microbiology and Clinical Biochemistry Laboratories in Training and Research Hospital, Kayseri, Turkey, between June 2012 and December 2012. All urine samples were from outpatients to exclude hospital acquired infections. Specimens from inpatients or outpatients who had been hospitalized within the previous month were excluded. Spot midstream urine samples (10 mL, n ⫽ 1000) collected in accordance with standard guidelines (detailed instructions for collection were provided) using a disposable, sterile, neutral container, screw lid (Firatmed® Sterile Urine Sampling Container) were randomly selected for the study. In newborn and infants, sterile urine collection bags were used. All urine samples were collected on the morning of the examination, processed within 2 hours after collection and within 30 minutes after their submission to the laboratory. Automated urine analysis and quantitative culture were applied to all specimens. Urine particles were detected and classified by FUS200, and the FUS200-assigned classifications were edited by laboratory technicians. WBC and bacteria were counted per high-power field (hpf, 400 ⫻ magnification). Counts in hpf correspond to particle/μL ⫻ 6.25. Samples were cultured by application of 10 μL urine on 5% blood agar and eosine methylene blue agar plates (Oxoid, UK). Cultures were incubated at 37°C for 24 hours. Bacterial counts were expressed as the number of colony-forming units (CFUs) per milliliter. Growth of ⬍ 104 CFUs/mL was considered negative, which is the standard for diagnosis in pediatric patients and patients admitted to the intensive care unit in our hospital. If there were three or more kinds of colonies without a dominant species, the urine was considered contaminated. The Vitek®II system (BioMérieux, Marcy l’Etoile, France) was used for identification of microorganisms.
Of 1000 specimens, 760 were female with a mean age of 28.7 years (range 0–83 years) and 240 were male with a mean age 31.0 years (range 0–84 years) who belonged to the following general groups: pediatrics (n ⫽ 451), nephrology (n ⫽ 248), family medicine (n ⫽ 88), internal medicine (n ⫽ 51), urology (n ⫽ 47), infectious diseases (n ⫽ 30), physical therapy and rehabilitation (n ⫽ 28), pediatric nephrology (n ⫽ 17), cardiology (n ⫽ 14), and others (n ⫽ 26). The samples from infants aged between 0 and 3 years and children aged between 4 and 16 years accounted for 7.7% and 38.1% of the total number of samples, respectively. Among the 1000 urine specimens submitted for culture, 637 cultures (63.7%) were negative, while significant microbiological growth was detected in 363 specimens (36.3%). Organisms isolated from 363 positive urine cultures and their numbers of cases are shown in Table I. As expected, Escherichia coli was found to be the most common pathogen (70%) in this study. Growth of three or more different colonies was considered as contaminated (n ⫽ 9, 0.9%) and excluded from the study. Unexpectedly, we detected that, of 363 positive urine cultures, 82 samples showed no bacteria in the automated urine analysis. The ROC curves for bacteria and WBCs counts are shown in Figure 1, in which culture results ⱖ 104 CFB/L were taken as the reference for significant bacteriuria. The area under the curve (AUC) for the bacteria and WBCs count were 0.71 (95% CI: 0.67–0.74) and, 0.72 (95% CI: 0.69–0.76) respectively. There was no significant difference between AUCs of bacteria and WBCs count (p ⫽ 0.308). The best cut-off values obtained from the ROC analysis were 16/μL for bacteriuria (sensitivity: 82.3%, specificity: 58%), and 34/μL for WBCs (sensitivity: 72.3%, specificity: 65.2%). PPV, NPV and accuracy rate at the best cut-off values for bacteria and WBCs were also determined, and the results are shown in Table II.
Statistical Analysis
Discussion
Statistical analysis was carried out by SPSS® 15.0 (Statistical Packages for Social Sciences; SPSS Inc,
The FUS200 is a new automated urine sediment analyzer for identification and counting of bright-field
Analytical performance of FUS200 Table I. Organisms isolated from 363 positive urine cultures.
Scand J Clin Lab Invest Downloaded from informahealthcare.com by University of Southern California on 04/09/14 For personal use only.
Microorganism Escherichia coli Klebsiella pneumonia Proteus spp. Staphylococcus coagulase negative Enterococcus faecalis Staphylococcus aureus Staphylococcus epidermidis Streptococcus agalactiae Pseudomonas aeruginosa Morganella morganii Streptococcus haemolyticus Citrobacter brakii Candida spp. Maya Citrobacter freundii Acinetobacter baumannii Kontaminasyon Total
Number of cases 255 25 18 14 8 8 6 4 5 3 3 1 1 1 1 1 9 363
digital images of the formed elements in urine. It can be connected to a urine strip chemistry analyzer to provide an integrated chemical and microscopic urinalysis workstation. In this retrospective study we evaluated the performance of the FUS200 in comparison with the urine culture method for screening urine samples for urinary system infections. In the present study, we used only urine specimens from outpatients. Since the specimens from patients who have been hospitalized have characteristics different from those of patients with community-acquired urinary-tract infections, due to antibiotics, catheters and etc. [5,6], these samples were excluded. The best cut-off point found in our study by comparing culture and bacterial count with the
Figure 1. Receiver operating characteristic curves for bacteria and WBCs cut-off values.
3
Table II. Analytical performance of FUS200 at the best cut-off values for bacterial and WBCs count in 1000 specimens with cases positive in culture (versus urine quantitative culture).
Sensitivity (%) Specificity (%) Positive Predictive Value (%) Negative Predictive Value (%) Accuracy Rate (%)
Bacterial count Cut-off 16/μL
WBCs count Cut-off 34/μL
82.3 58.0 65.0 77.5 73.5
72.3 65.2 57.1 78.5 69.7
FUS200 was 16 bacteria/μL (Table II). This value is significantly lower than the data reported on previous studies for different automated urine sediment analyzers. To the best of our knowledge, analytic performance of the FUS200 has not so far been researched. Earlier studies which have shown cut-off values have demonstrated ranges between 125–170 bacteria/μL for UF-1000i [3,7,8], 1000–6000 bacteria/μL for UF-100 [2,9–11] and 85 bacteria/μL for UriSed. During the data collection for this study, we detected that 82 urine samples with positive cultures had no bacteria in the automated urine analysis. This may lead to consideration of bacteria identification and quantification problem of the FUS200. An optimal screening method must ensure primarily a high sensitivity and a NPV in ruling out the diagnosis of a urinary-tract infection. The European Urinalysis Guidelines recommend an analytical sensitivity ⬎ 90–95% to detect bacteriuria at 105 CFU/mL by a rapid non-culture method with a confirmatory culture of positive cases [12]. At a cut-off value of 16 bacteria/μL, the sensitivity was 82.3%, NPV 77.5%, and the percentage of samples that did not need to be cultured was 65%. These sensitivity and NPV values are lower than the recommendation of The European Urinalysis Guidelines. We also evaluated the sensitivity, specificity, PPV, and NPV for WBCs because the presence of leukocytes is crucial in urinary system-infection diagnosis and the evaluation of the success of treatment [13]. The best cut-off value obtained by ROC analysis was 34 WBCs/μL with the sensitivity of 72.3% and NPV of 78.5%. This result was similar to the data reported in previous studies for different automated urine sediment analyzers [2,9–11,14]. As shown by the ROC curve analysis in this study (Figure 1), diagnostic values of bacteria and leukocytes were similar (AUC: 0.710 and 0.728 respectively, p ⫽ 0.308). Since the cut-off values of bacteria and WBC counts may change due to the patient population, the type of specimens and the selected threshold for significant counts in culture, each laboratory must examine and report these values [3]. Also, because different automated systems report
Scand J Clin Lab Invest Downloaded from informahealthcare.com by University of Southern California on 04/09/14 For personal use only.
4
D. Kocer et al.
different cut-off values for bacteria and WBC counts due to the analyzing method, physicians should know the system used in their laboratory for urine analysis and assess the results with respect to the cut-off values of their own analyzer used. In the present study, the main purpose of screening urine specimens was to find out if it is possible to predict positive cultures and thereby eliminate the negative cultures rapidly and safely. The most important requirement of a rapid diagnostic screening test is sensitivity, and, in this perspective, an unsatisfactory sensitivity by using bacteria recognition and quantification performed by the FUS200 analyzer has been observed. According to the manufacturer, the FUS200 is able to detect and classify erythrocytes, leukocytes and squamous epithelial cells. However, for other elements in urine it is recommended to review images on-screen by trained laboratory personnel to make a definitive diagnosis. So this problem may also be related to ineffective identification by laboratory technicians. After further technical improvements in particle recognition and laboratory personnel training, the FUS200 might show better results.
Acknowledgements None to declare.
Declaration of interest: The authors have no conflicts of interest. The authors alone are responsible for the content and writing of the paper. References [1] Fogazzi GB, Ponticelli C, Ritz E. The urinary sediment in the main diseases of the urinary tract. In: Fogazzi GB, Ponticelli C, Ritz E, editors. The urinary sediment: an integrated view. 2nd edn. Oxford: Oxford University Press; 1999. pp. 139–60.
[2] Zaman Z, Roggeman S, Verhaegen J. Unsatisfactory performance of flow cytometer UF-100 and urine strips in predicting outcome of urine cultures. J Clin Microbiol 2001;39:4169–71. [3] De Rosa R, Grosso S, Bruschetta G, Avolio M, Stano P, Modolo ML, Camporese A. Evaluation of the Sysmex UF1000i flow cytometer for ruling out bacterial urinary tract infection. Clinica Chimica Acta 2010;411:1137–42. [4] Karakukcu C, Kayman T, Ozturk A, Torun YA. Analytic performance of bacteriuria and leukocyturia obtained by UriSed in culture positive urinary tract infections. Clin Lab 2012;58:107–11. [5] Foxman B. Epidemiology of urinary tract infections: incidence, morbidity, and economic costs. Am J Med 2002; 113(Suppl. 1A):5S–13S. [6] Jones RN. Impact of changing pathogens and antimicrobial susceptibility patterns in the treatment of serious infections in hospitalized patients. Am J Med 1996; 100:3S–12S. [7] Manoni F, Fornasiero L, Ercolin M, Tinello A, Ferrian M, Hoffer P, Valverde S, Gessoni G. Cutoff values for bacteria and leukocytes for urine flow cytometer Sysmex UF-1000i in urinary tract infections. Diagn Microbiol Infect Dis 2009; 65:103–7. [8] Wang J, Zhang Y, Xu D, Shao W, Lu Y. Evaluation of the Sysmex UF-1000i for the diagnosis of urinary tract infection. Am J Clin Pathol 2010;133:577–82. [9] Evans R, Davidson M, Sim L, Hay A. Testing by Sysmex UF-100 flow cytometer and with bacterial culture in a diagnostic laboratory – a comparison. J Clin Pathol 2006; 59:661–2. [10] Koken T, Aktepe O, Serteser M, Samli M, Kahraman A, Dogan N. Determination of cut-off values for leukocytes and bacteria for urine flow cytometer (UF-100) in urinary tract infection. Int Urol Nephrol 2002;34:175–8. [11] Manoni F, Valverde S, Antico F, Salvadego M, Giacomini A, Gessoni G. Field evaluation of a second generation cytometer UF-100 in diagnosis of acute urinary tract infections in adult patients. Clin Microbiol Infect 2002;8:662–8. [12] European Confederation of Laboratory Medicine. European urinalysis guidelines. Scand J Clin Lab Invest 2000; 231(Suppl.):1–86. [13] Ottiger C, Schaer G, Huber AR. Time-course of quantitative urinary leukocyte bacteria counts during antibiotic therapy in women with symptoms of urinary tract infection. Clin Chim Acta 2007;379:36–41. [14] Kayalp D, Dogan K, Ceylan G, Senes M, Yucel D. Can routine automated urinalysis reduce culture requests? Clin Biochem 2013;46:1285–9.
