Urine analysis performed by flow cytometry: reference range determination and comparison to morphological findings, dipstick chemistry and bacterial culture results - A multicenter study

Aim: To validate whether quantitative flow-cytometric analysis of particula te matter in urine would allow for accurate and rapid enumeration of red bl ood cells (RBC), leukocytes (WBC), squamous epithelial cells (EC), casts, a nd bacteria, a Sysmex UF-100 analyzer was tested in a multicenter study. Ma terial and methods: At first, reference values were established and found t o be < 14 for RBC, < 16 for WBC, < 9 for EC, < 2 for casts and < 173 for ba cteria, respectively (counts per mul; 97.5 percentile). Due to the wide use of dipstick and microscopic sediment analysis in routine urine diagnostics , comparative studies on 950 random urine samples were performed. Bacterial counting combined with WBC enumeration was further compared in 266 routine urinary microbiologic cultures. Results: Good correlations were found comp aring UF-100 results of RBC (r = 0.89), WBC (r = 0.94), and EC (r = 0.74) w ith Fuchs-Rosenthal Chamber (FRC) counts. However, some misclassification o f casts (r = 0.32) could be observed. Correlations of UF-100 with dipstick and sediment testing was significant (p < 0.001), but the scatter of the la tter two methods is too wide to consider them as quantitative methods. Prom ising results further revealed that the analyzer has a good negative predic tive value (NPV) for microbiologically negative cultures, especially for cu ltures with bacterial counts of 10(5)/l (NPV = 95%). Conclusion: The analyz er is capable of providing rapid and reliable urine analysis of cellular pa rticles avoiding the known imprecision of dipstick and sediment methodology . Thus, when used in an algorithm, combined with dipstick or quantitative u rine chemistry analysis (for hemoglobin, esterase, protein, glucose, etc.), this analyzer might serve as a rapid and accurate screening tool in routin e urine analysis, thereby reducing manual reviewing rate as well as the num ber of missed samples, compared to screening with dipstick alone.