Usefulness of urinalysis and urine gram stain in the diagnosis of urinary tract infection in hospitalized patients

Abstract

OBJECTIVE: To evaluate the usefulness of urinalysis and of urine Gram stain in the diagnosis of urinary tract infection in hospitalized patients.

DESIGN AND SAMPLE: Urinalysis and Gram stain of non centrifuged urine were carried out according to the requests of physicians, in specimens submitted to the laboratory for urine culture. When this modality of Gram stain had not been requested, it was done with urine sediment. Results were compared with those of the culture.

RESULTS: Ten thousand nine hundred and seventeen urine cultures were carried out, as well as 6.762 urinalyses, 2.762 Gram stains of non centrifuged urine, and 8.008 Gram stains of urine sediments. In comparison with the urine culture, urinalyses had 99% sensitivity, 51% specificity, 60% positive predictive value, and 98% negative predictive value. Gram stain of non centrifuged urine had 98% sensitivity, 73% specificity, 82% positive predictive value, and 97% negative predictive value. Gram stain of urine sediment had 95% sensitivity, 78% specificity, 67% positive predictive value, and 97% negative predictive value.

CONCLUSIONS: Urinalysis, following well defined criteria, and Gram stain have high negative predictive values, that may allow to use them as screening tests to determine the need to request urine culture.