Does it matter how you collect urine when diagnosing UTI?

Which urine collection methods do office-based pediatricians use to diagnose urinary tract infection in young, febrile infants? What characteristics of infants and practitioners predict the urine collection method that is chosen? And do the diagnostic test characteristics of urinalysis and urine culture differ when comparing bag and urethral catheterization methods?

To address these questions, investigators prospectively analyzed the performance of urine testing (urinalysis and urine culture) in more than 3,000 infants as old as 3 months who had a temperature of ≥38° C. Subjects came from more than 200 practices within the Pediatric Research in Office Settings (PROS) network.

Of the 1,646 patients whose urine specimen was obtained on the day of presentation, approximately 70% underwent catheterization; 30%, bag testing. Catheterization was most likely to be used when a patient was severely dehydrated, covered by a Medicaid plan, or seen after hours, or was female. Younger practitioners (l40 years) were most likely to favor catheterization over bag testing.

Commentary Bagging may be easier than catheterizing an infant, but there's a trade off: You need to decide if the greater ease is worth the 1-in-21 chance that the culture result will be confusing.

Stakes get higher when you want to start empiric therapy for fever in these babies. (According to an earlier report on this PROS population sample, practitioners started antibiotics at the time of the first evaluation more than 50% of the time [JAMA 2004;291:1203].) Once antibiotics are started, repeat cultures are invalid and you may be obliged to complete treatment and perform an imaging study of the child's urinary tract.

The study provides other helpful information: