Urinalysis identifies the youngest infants with UTIs

Urinalysis is extremely sensitive and specific for screening for urinary tract infections (UTIs) in febrile infants aged 60 days and younger, especially when the UTI is associated with bacteremia, a recent study showed.

Investigators evaluated the test characteristics of the urinalysis in aggregate and of 3 individual components-leukocyte esterase (LE), nitrites, and pyuria-for diagnosing UTIs with and without associated bacteremia. They used 2 definitions of UTI: growth of 50,000 or more or of equal to or greater than 10,000 colony-forming units (CFU) per mL of a pathogen.

The study was in almost 4500 febrile infants aged 60 days or younger from whom blood cultures were obtained as part of an emergency department evaluation for bacterial infection; 289 (7%) had UTIs with equal to or greater than 50,000 CFU/mL, including 27 (9.3% of the 289) with bacteremia. A positive urinalysis showed perfect sensitivity when accompanied by bacteremia (100%) and an excellent 94% sensitivity without bacteremia. Specificity was 91%. For UTIs defined by colony counts equal to or greater than 10,000 CFU/mL, sensitivity of the urinalysis was 87% and specificity 91%.

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Most infants with UTIs had urinalyses positive for LE or pyuria, although nitrites generally were absent irrespective of UTI status. All patients with UTIs with bacteremia had either moderate or large concentrations of LE. Infants without bacteremia whose urine colony counts were below 100,000 CFU/mL were less likely than infants with higher counts to have LE, nitrites, or pyuria (Tzimenatos L, et al. Pediatrics. 2018;141[2]:e20173068).

Thoughts from Dr. Burke

My takeaway here is that the urinalysis is often predictive of a UTI, even in a very young child, but, as with any test, we need to leave room for some clinical judgment when deciding which febrile infants have a UTI. No test is perfect.