Sensitivity and specificity of urinalysis samples in critically ill patients

Pre-emptive screening of urine for patients admitted to an intensive care unit can result in the misinterpretation of data and over- or under-treatment of urinary tract infection.

Data were studied from 169 consecutive patients admitted to the neurologic or burn intensive care unit at Shands Hospital at the University of Florida. All patients had a urinary catheter in place at the time of admission. Urinalysis and urine culture were sent for analysis. Data included leukocyte esterase, urine nitrate, urine protein, pyuria or urine white blood cell count, and culture.

Leukocyte esterase and pyuria were the most sensitive indicators of a positive urine culture at 87.5% (95% CI: 71.3-100%) and 73.3% (95% CI: 51.0-95.7%), respectively; urine nitrate was specific at 100%. More than half of the patients (56.3%) with positive cultures did not initially receive antibiotics.

The combination of leukocyte esterase and urine nitrate provides the best indicator for the initiation of antibiotic coverage for urinary tract infection prior to culture availability.