Disappointing dipstick screening for urinary tract infection in hospital inpatients

Abstract

Aim - To compare the performance of leucocyte esterase and nitrite dipstick tests with microscopic examination and culture of first morning urines (n = 420) of hospital inpatients. Results - The sensitivity, specificity, and negative predictive value of the leucocyte esterase test for the cutoff of > 10 WBC/μl were 57%, 94%, and 68%, respectively. For > 5 WBC per high power field (HPF) these variables were 84%, 90%, and 93%. For > 105 colony counts/ml, the sensitivity of the nitrite test was 27%, specificity 94%, and negative predictive value 87%. When either leucocyte esterase or nitrite positivity was accepted as a marker of urinary tract infection, the sensitivity was 78%, specificity 75%, and negative predictive value 94%, and there were 22% false negative results. Semiquantitative microscopic estimation of bacteria per HPF yielded 40% false positives. Conclusions - Leucocyte esterase and nitrite dipstick tests are not suitable for screening for urinary tract infections.