The nitrite and leukocyte esterase tests for the evaluation of asymptomatic bacteriuria in obstetric patients

The purpose of this investigation was to compare the reliability of a urine dipstick evaluation for nitrites and leukocyte esterase activity with that of a urine culture in diagnosing asymptomatic bacteriuria in obstetric patients. A clean-catch midstream urine specimen was obtained from 750 consecutive obstetric patients presenting for initial evaluation. One portion of the specimen was tested for nitrites and leukocyte esterase activity with Chemstrip LN dipsticks. A second aliquot of urine was plated on blood and MacConkey agar and incubated aerobically. The cost of the nitrite and leukocyte esterase test was $0.35. The per patient charge for the urine cultures would have been $28. Sixty-two women (8.3%) had urine cultures of 100,000 or more colony-forming units of a uropathogen per milliliter. The sensitivities of the nitrite and leukocyte esterase test in identifying patients with positive cultures were 43 and 77%, respectively, and the specificities were 99 and 96%, respectively. The sensitivity and specificity for the two tests combined (either test abnormal) were 92 and 95%, respectively. Five patients had negative screening tests but positive urine cultures; all five isolates were gram-positive organisms, three group B streptococci and two enterococci. We conclude that neither the nitrite test nor the leukocyte esterase test alone is a sensitive enough screening test to detect asymptomatic bacteriuria in obstetric patients. The combination of the two tests, however, may provide an acceptable cost-effective alternative to screening all asymptomatic obstetric patients with urine cultures.