Accuracy of the Urinalysis for Urinary Tract Infections in Febrile Infants 60 Days and Younger

OBJECTIVES: Reports of the test accuracy of the urinalysis for diagnosing urinary tract infections (UTIs) in young febrile infants have been variable. We evaluated the test characteristics of the urinalysis for diagnosing UTIs, with and without associated bacteremia, in young febrile infants. METHODS: We performed a planned secondary analysis of data from a prospective study of febrile infants ≤60 days old at 26 emergency departments in the Pediatric Emergency Care Applied Research Network. We evaluated the test characteristics of the urinalysis for diagnosing UTIs, with and without associated bacteremia, by using 2 definitions of UTI: growth of ≥50 000 or ≥10 000 colony-forming units (CFUs) per mL of a uropathogen. We defined a positive urinalysis by the presence of any leukocyte esterase, nitrite, or pyuria (>5 white blood cells per high-power field). RESULTS: Of 4147 infants analyzed, 289 (7.0%) had UTIs with colony counts ≥50 000 CFUs/mL, including 27 (9.3%) with bacteremia. For these UTIs, a positive urinalysis exhibited sensitivities of 0.94 (95% confidence interval [CI]: 0.91–0.97), regardless of bacteremia; 1.00 (95% CI: 0.87–1.00) with bacteremia; and 0.94 (95% CI: 0.90–0.96) without bacteremia. Specificity was 0.91 (95% CI: 0.90–0.91) in all groups. For UTIs with colony counts ≥10 000 CFUs/mL, the sensitivity of the urinalysis was 0.87 (95% CI: 0.83–0.90), and specificity was 0.91 (95% CI: 0.90–0.92). CONCLUSIONS: The urinalysis is highly sensitive and specific for diagnosing UTIs, especially with ≥50 000 CFUs/mL, in febrile infants ≤60 days old, and particularly for UTIs with associated bacteremia.