Urine flow cytometry as a primary screening method to exclude urinary tract infections.
ABSTRACT PURPOSE: To exclude urinary tract infections, culture is the gold standard method, although it is time consuming and costly. Current strategies using dipstick analysis are unsatisfactory as screening methods, because of inadequate sensitivity/specificity. Urine flow cytometry is an attractive alternative. To exclude urinary tract infections, a cutoff value to screen for negative cultures was determined. METHODS: 281 outpatients (51 % male) of a general population visiting the urology department were included. Urine samples were measured by flow cytometry and compared with culture results and dipstick analysis. ROC analysis was performed to evaluate the screening performance of flow cytometry and dipstick analysis compared to culture. RESULTS: 18 % of cultures were positive, defined as >10(4) colony forming units/mL. Bacterial count by flow cytometry alone provides the best sensitivity and specificity to exclude a urinary tract infection. A cutoff value of 60 bacteria/μL urine leads to a sensitivity of 100 % and a specificity of 60 %. Retrospectively, with a cutoff value of 60 bacteria/μL urine, 49 % of the cultures would have been redundant. 20 % of patients receiving antibiotics possibly had received those unnecessarily. The calculated percentage of false negatives was 0 % (95 % confidence interval 0-3.3 %). CONCLUSIONS: Urine flow cytometry is a reliable screening method to exclude urinary tract infections. With a cutoff value of 60 bacteria/μL urine, negative predictive value is 100 % and the calculated percentage of false negatives is 0 % (95 % confidence interval 0-3.3 %). Using flow cytometry as a screening method could lead to a reduction in cultures and antibiotics.
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ABSTRACT: Automation and standardization of sediment analysis of urine samples by flow cytometry might serve as an alternative to labor-intensive laboratory methods, such as microscopic examination and culture. The Sysmex UF-1000i is a urine flow cytometer that uses two separate channels for counting blood cells and bacteria. In this study, 358 urine samples were analyzed with the Sysmex UF-1000i in parallel with manual microscopy, Gram stain and bacterial culture, the latter considered the gold standard. Reproducibility for detection of white and red blood cells and bacteria was good, while detection of yeast proved unreliable. Depending on the definition of urinary tract infection (UTI) used, the negative predictive value and the percentage of false-negative results were 100% and 0% [UTI ≥ 10(5) colony forming units (CFU)/mL] and 99% and 1.3%, (UTI ≥ 10(4) CFU/mL), respectively. Pre-screening with the Sysmex UF-1000i would have resulted in a reduction of bacterial culture by 42%. Carry over of bacteria between consecutive samples due to the use of fixed sample needle was observed, but did not result in false-positive interpretation of Sysmex UF-1000i results. Because of the occurrence of carry over, samples that have been analyzed with the Sysmex UF-1000i cannot be used for subsequent urine culture. In conclusion, the Sysmex UF-1000i offers the possibility for screening high numbers of urine samples in a fast and standardized way, resulting in a reduction in workload and speeding the diagnostic process. It is not recommended for use in complicated patient populations, such as neutropenic patients and patients in whom yeast infection is suspected.Clinical Chemistry and Laboratory Medicine 12/2010; 48(12):1765-71. · 3.01 Impact Factor
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ABSTRACT: Urinary tract infection (UTI) is a widespread disease, and thus, the most common samples tested in diagnostic microbiology laboratories are urine samples. The "gold standard" for diagnosis is still bacterial culture, but a large proportion of samples are negative. Unnecessary culture can be reduced by an effective screening test. We evaluated the performance of a new urine cytometer, the Sysmex UF-1000i (Dasit), on 703 urine samples submitted to our laboratory for culture. We compared bacteria and leukocyte (WBC) counts performed with the Sysmex UF-1000i to CFU-per-milliliter quantification on CPS agar to assess the best cutoff values. Different cutoff values of bacteria/ml and WBC/ml were compared to give the best discrimination. On the basis of the results obtained in this study, we suggest that when the Sysmex UF-1000i analyzer is used as a screening test for UTI the cutoff values should be 65 bacteria/ml and 100 WBC/ml. Diagnostic performance in terms of sensitivity (98.2%), specificity (62.1%), negative predictive value (98.7%), positive predictive value (53.7%), and diagnostic accuracy (73.3%) were satisfactory. Screening with the Sysmex UF-1000i is acceptable for routine use. In our laboratory, we have reduced the number of bacterial cultures by 43%, speeded up their reporting, and decreased the inappropriate use of antibiotics.Journal of clinical microbiology 11/2010; 48(11):3990-6. · 4.16 Impact Factor
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ABSTRACT: Urine samples constitute a large proportion of samples tested in clinical microbiology laboratories. Culturing of the samples is fairly time- and labor-consuming, and most of the samples will yield no growth or insignificant growth. We analyzed the feasibility of the flow cytometry-based UF-500i instrument (Sysmex, Japan) to screen out urine samples with no growth or insignificant growth and reduce the number of samples to be cultured. A total of 1,094 urine specimens sent to our laboratory for culture during 4 months in the spring of 2009 in Lahti, Finland, were included in the study. After culture, all samples were analyzed with the Sysmex UF-500i for bacterial and leukocyte (white blood cell [WBC]) counts. Youden index and closest (0,1) methods were used to determine the cutoff values for bacterial and WBC counts in culture-positive and -negative groups. By flow cytometry, samples considered positive for UTI in culture had bacterial and WBC values that were significantly higher than those for samples considered negative. The flow cytometric screening worked best when both bacterial counts and WBC counts were used with age- and gender-specific cutoff values for all patient groups, excluding patients with urological disease or anomaly. By use of these cutoff values, 5/167 (3.0%) of culture-positive samples were missed by UF-500i and the percentage of samples that did not need to be cultured was 64.5%. Use of the UF-500i instrument is a reliable method for screening out a major part of the UTI-negative samples, significantly diminishing the amount of work required in the microbiology laboratory.Journal of clinical microbiology 09/2010; 48(9):3117-21. · 4.16 Impact Factor