Screening of Urine Samples by Flow Cytometry Reduces the Need for Culture

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.Urinary tract infections (UTIs) are among the most common infections treated by community health care centers and hospitals (5,6,13,19,24). In Finland, urinary tract infections account for approximately 6% of all infectious disease diagnoses in primary care (20) and urine samples constitute a large proportion of the samples tested in clinical microbiology laboratories (13,18,24). The gold standard for UTI diagnosis is bacterial culture, which is based on bacterial counts and identification. Culturing of the samples is fairly time-and laborconsuming, and most of the samples yield no growth or insignificant growth (10,15,22,24). In order to improve the efficiency of handling of the urine samples, methods for screening out the culture-negative samples from the culture-positive samples have been developed. Chemical screening with strips for nitrite, pH, leukocytes, erythrocytes, albumin, and glucose is widely used (17,18,22,23), but a meta-analysis of the literature (4) has shown that the method is insensitive and is suitable as a rule-out test only when both nitrite and leukocyteesterase are negative. Cells, particles, and microorganisms in urine can be examined by microscopic-urine-sediment analysis, but this method is time-consuming, labor-intensive, and sensitive to interobserver variability (2,7,8,10,12,21).Pyuria with bacteria predicts bladder infection better than the presence of bacteria alone, and therefore, a screenin...

Bacteriuria Screening by Automated Whole-Field-Image-Based Microscopy Reduces the Number of Necessary Urine Cultures

“…Table 2 indicates the distribution of urine sediment results according to the criteria used for classifying positive samples compared to urine culture results with corresponding bacterial quantification. The prevalence of UTI in our study was 18.3%, similar to that obtained by other authors (Jolkonnen et al [10], 16.8%, and Manoni et al [12], 20.71%), and pathogen distribution was also in good agreement with data from the literature (6).…”

Flow Cytometry Analysis Using Sysmex UF-1000i Classifies Uropathogens Based on Bacterial, Leukocyte, and Erythrocyte Counts in Urine Specimens among Patients with Urinary Tract Infections

“…The first-generation automated FCA instrument, Sysmex UF50 (Medical Electronics, Kobe, Japan) showed variable results, but the next-generation Sysmex UF-500i and UF-1000i instruments have improved sensitivity and specificity, as well as a separate measurement channel for detecting bacteria (15)(16)(17)(18)(19). In urine specimens, FCA identifies and enumerates bacteria, leukocytes, erythrocytes, and other cells.…”

“…In urine specimens, FCA identifies and enumerates bacteria, leukocytes, erythrocytes, and other cells. Culture-negative specimens are identified and ruled out before culture is performed, which reduces the turnaround time, workload, and cost (15)(16)(17). However, the instrument has not been evaluated for its ability to predict uropathogens prior to urine culture.…”

Automated urinalysis: First experiences and comparison of automated urinalysis system and manual microscopy

“…[9][10][11] Conventional microscopic analysis of urine sediments although considered to be the reference method, in values several methodological steps such a centrifugation and discarding that lead to loss and destruction of cells and result in imprecision and inaccuracy. 6 These procedures are not required in the automated analysis.…”