The Use of Gram Stain and Leukocyte Esterase/Nitrite Test Strips for the Detection of Bacteriuria

Abstract

Two hundred seventy urine specimens were used to evaluate the leukocyte esterase-nitrite tests and urine Gram stain as screening procedures for the detection of significant bacteriuria. The data indicated that the combination of leukocyte esterase plus nitrite offered the more effective screening method when compared with culture. The combination demonstrated a sensitivity and specificity of 94.4% and 56.9%, respectively, and positive and negative predictive values of 54.8% and 94.9%, respectively, with ≥105 organisms mL as a definition of significant bacteriuria. If ≥104 organisms mL were the working definition of significant, the sensitivity, specificity, and positive and negative predictive values were 87.5%, 52.7%, 37.1%, and 93.2%, respectively. The addition of the Gram stain screen did not significantly alter either the specificity or the negative predictive value. However, because there are patient populations where ≥104 organisms/mL or ≥105 organisms/mL may not be the accurate indication of significant bacteriuria, the leukocyte esterase and nitrite tests should be used cautiously and only in carefully selected clinical conditions.