The usefulness of screening tests for pyuria in combination with culture in the diagnosis of urinary tract infection.

A prospective study was conducted to examine the usefulness of screening tests for pyuria in combination with culture in the diagnosis of urinary tract infection (UTI) in outpatients. Midstream urine specimens were collected from 340 patients seen in the emergency treatment center (ETC) and were examined for pyuria using the chamber count method and the Leukocyte Esterase Dipstick test (LE; Bio Dynamics, Indianapolis, IN). All specimens were cultured quantitatively using both 0.01 ml and 0.001 ml calibrated bacteriologic loops. A total of 100 UTIs, defined by combined clinical and laboratory critera, were identified. Sixty-four (64%) infections were identified by culture using the standard interpretive breakpoint of greater than or equal to 10(5) CFU/ml and an additional 36 (36%) were detected using the low-count interpretive breakpoint of greater than or equal to 10(3) CFU/ml. We found pyuria detection by either the chamber count method or the LE test to be extremely useful in directing subsequent culture efforts. By using either of the tests for pyuria to determine the significance of low-count bacteriuria (10(3) - less than 10(5) CFU/ml) we were able to achieve maximum sensitivity (92%-99%) and specificity (99.2-99.6%) for the diagnosis of UTI while minimizing the number of specimens in which low numbers of organisms must be evaluated.