Objective: To determine the predictors and results of urine testing of young febrile infants seen in office settings.

Design: Prospective cohort study.

Setting: Offices of 573 pediatric practitioners from 219 practices in the American Academy of Pediatrics Pediatric Research in Office Settings' research network.

Subjects: A total of 3066 infants 3 months or younger with temperatures of 38 degrees C or higher were evaluated and treated according to the judgment of their practitioners.

Main outcome measures: Urine testing results, early and late urinary tract infections (UTIs), and UTIs with bacteremia.

Results: Fifty–four percent of the infants initially had urine tested, of whom 10% had a UTI. The height of the fever was associated with urine testing and a UTI among those tested (adjusted odds ratio per degree Celsius, 2.2 for both). Younger age, ill appearance, and lack of a fever source were associated with urine testing but not with a UTI, whereas lack of circumcision (adjusted odds ratio, 11.6), female sex (adjusted odds ratio, 5.4), and longer duration of fever (adjusted odds ratio, 1.8 for fever lasting > or = 24 hours) were not associated with urine testing but were associated with a UTI. Bacteremia accompanied the UTI in 10% of the patients, including 17% of those younger than 1 month. Among 807 infants not initially tested or treated with antibiotics, only 2 had a subsequent documented UTI; both did well.

Conclusions: Practitioners order urine tests selectively, focusing on younger and more ill–appearing infants and on those without an apparent fever source. Such selective urine testing, with close follow–up, was associated with few late UTIs in this large study. Urine testing should focus particularly on uncircumcised boys, girls, the youngest and sickest infants, and those with persistent fever.