Clinical usefulness of iQ200/iChem Velocity workstation for screening of urine culture

BackgroundClinical microbiology laboratories are asked to process large numbers of urine specimens for culture, but only 20-40% of them are positive. Therefore, a rapid, reliable screening method is necessary to speed up the reporting of a negative result. In this study, we evaluated the iQ200/iChem workstation, which is a combination of digital imaging software and a strip reader to predict negative urine culture.MethodA total of 1942 urine specimens were processed through both culture and iQ200/ iChem workstation. We analyzed the performance using two definition of positive urine culture; one or two potential uropathogens at a concentration of 10(5)CFU/ml and10(4)CFU/ml. We assessed combinations of parameters (ASP; all small particles, WBC; leukocyte, BACT; bcteria, LE; leukocyte esterase) applying various cut-offs which can achieve the negative predictive value (NPV) 97% and culture reduction rate50%.ResultsThe culture positive rate was 12.8 and 18.4% applying the criteria of 10(5)CFU/ml and10(4)CFU/ml, respectively. The area under the curve (AUC) of each parameter for 10(5)CFU/ml / 10(4)CFU/ml bacteriuria was 795 /0.719 for WBC, 0.722 / 0.701 for ASP and 0.740 /0.704 for bacteria. Therefore, we investigated the combination of the parameters. With the fixed parameter of BACT1/HPF and positive LE, the combinations of WBC4/HPF and ASP 8500/l or WBC6/HPF and ASP5500/l showed good performance for detecting 10(5)CFU/ml uropathogen. The ranges of sensitivity, specificity, negative predictive value and culture reduction rate were 91.5-92.3%, 49.8-52.6%, 97.7-97.9% and 50.4-53.0%, respectively. However, none of the combined setting yielded acceptable range of NPV for detecting 10(4)CFU/ml uropathogen (NPV 92.9-94.9%). Enterococcus spp. was the most common uropathogen causing the false negative results (55.7%), and also the main pathogen among the positive culture of 10(4-5)CFU/ml bacteriuria (45%).ConclusionsiQ200/iChem workstation was excellent in detection of 10(5)CFU/ml uropathogen, but unsatisfactory in detection of 10(4-5) CFU/ml uropathogen and Enterococcus spp. It can be useful for screening of urine specimens to reduce bacterial culture. However, notice from clinician will be necessary for specimens from the patients with high risk for UTI, such as pregnant woman, infant, elderly or immune compromised patients.