Reflex Testing of Male Urine Specimens Misses Few Positive Cultures May Reduce Unnecessary Testing of Normal Specimens

Abstract

To determine the predictive values of leukocyte count for the presence of a positive urine culture in ambulatory male urology patients. Many institutions have adopted a practice of "reflex testing" urine samples, in which urine culture is only performed if a threshold number of leukocytes (WBCs [white blood cells]) is present. We performed a retrospective chart review of all male patients who presented to our tertiary-care urology clinic in 2006. Only those with both a urinalysis and urine culture performed were included in this study. A urine culture was considered positive if at least 10,000 colonies of a uropathogen were present. Data were tabulated and analyzed using SPSS V15.0 software. Of 874 patients, 176 (20%) urine cultures were positive. WBCs were present at a concentration of at least 5/hpf (high power field) in 367 (42%) of all specimens and in 163 of 176 (93%) positive specimens, but were present at lower concentrations in 13 specimens with positive cultures. The presence of >5 WBC/hpf had a positive predictive value of 47%, and a negative predictive value of 97% for positive culture. Reflex urine testing, in which cultures are done on urine specimens with >5 WBC/hpf, would have missed 7% of positive urine cultures, while avoiding 69% of all cultures. Reflex testing may be appropriate in most ambulatory urology patients.