A study of various tests to detect asymptomatic urinary tract infections in an obstetric population

To compare rapid screening techniques for detecting asymptomatic urinary tract infections (AUTIs) in pregnant women.

Comparison of results of the screening tests of urinalysis, urine dipstick, and Gram's staining with the results of standard urine culture at an initial prenatal visit. In follow-up visits, urine dipstick testing was compared with urinalysis.

Departments of Family Medicine and Obstetrics and Gynecology, Mayo Clinic, Rochester, Minn.

Pregnant women (1047) from the local community were screened for AUTI on initial and follow-up visits.

Initial prenatal urine was tested by using urine dipstick testing, urinalysis, Gram's staining, and urine culture. At each follow-up visit, urine specimens were tested by using urine dipstick and urinalysis.

Sensitivity and specificity, incremental patient costs, and clinical outcomes were used to assess the effectiveness of the techniques.

On initial visits, rapid screening tests for AUTI in pregnant women revealed the following: Gram's staining identified 22 of 24 patients with AUTI (sensitivity, 91.7%; specificity, 89.2%); urine dipstick, 12 of 24 (sensitivity, 50.0%; specificity, 96.9%); and urinalysis with presence of leukocytes, six of 24 (sensitivity, 25.0%; specificity, 99.0%). In follow-up visits, urine dipstick tests detected 19 infections and urinalysis, three (positive predictive value, 5% compared with 3%).

Urine dipstick testing for nitrites identified half of all patients with urinary tract infections and was superior to urinalysis on follow-up visits. Although Gram's staining is more expensive, it was more accurate for AUTI than urinalysis or urine dipstick test for nitrites. Urinalysis was never the test of choice because it was more expensive and detected fewer positive cultures. Leukocyte measurement correlated poorly with AUTI.