Reflex Testing of Male Urine Specimens Misses Few Positive Cultures May Reduce Unnecessary Testing of Normal Specimens
Received 16 July 2009; accepted 29 August 2009. published online 16 November 2009.
Objectives
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.
Methods
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.
Results
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.
Conclusions
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.
aDepartment of Urology, Loyola University Medical Center, Maywood, Illinois
bDepartment of Pathology, Loyola University Medical Center, Maywood, Illinois
Reprint requests: Cynthia Fok, M.D., Fahey Building, Loyola University Medical Center, 2160 S First Ave, Maywood, IL 60153
ABSTRACT