Aggregate urinalysis (UA) is highly sensitive and specific in identifying urinary tract infections (UTI) in febrile young infants 60 days of age or younger, with or without associated bacteremia (Pediatrics 2018;14:e20173068). The findings clarify the utility of UA in this population, after prior studies showed variable test performance.

About 90% of serious bacterial infections in babies 60 days of age or younger arise from UTIs. Yet prior studies evaluating the performance of UA in this patient group reported sensitivities ranging from 48% to 99% and specificities ranging from 88% to 98%. American Academy of Pediatrics clinical practice guidelines provide recommended UA bacteremia thresholds for children 2 months to 2 years of age, but not for newborns.

The study involved 4,147 infants treated at 26 emergency departments. The researchers set two definitions of UTI: growth of ≥50,000 or ≥10,000 colony-forming units (CFUs) per mL of a uropathogen. They defined a positive UA as presence of any leukocyte esterase, nitrite, or pyuria (classified as >5 white blood cells per high-power field). Participating labs performed UA according to established methods and procedures at each facility.

Overall, 7% of subjects had UTIs with colony counts ≥50,000 CFUs/mL, 9.3% of whom had bacteremia. The investigators established an overall 0.94 sensitivity, 0.91 specificity, and 1.00 negative predictive value (NPV) for positive UAs regardless of bacteremia. In the presence of bacteremia, sensitivity rose to 1.00 with no change in specificity or NPV. Sensitivity of UA in detecting UTI dropped to 0.87 regardless of bacteremia status when the researchers considered a growth threshold of 10,000 CFUs/mL rather than 50,000 CFU/mL. However, sensitivity remained the same at 1.00.