Diagnosis of Bacteriuria and Leukocyturia by Automated Flow Cytometry Compared with Urine Culture

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.