The reported accuracy of the urinalysis (UA) for diagnosing urinary tract infections (UTI) is febrile infants ≤ 60 days has been widely variable. Some guidelines specifically exclude these patients due to this variability or recommend urine culture as the primary test.1
Accuracy of the Urinalysis for Urinary Tract Infections in Febrile Infants 60 Days and Younger, published in Pediatrics in February of 2018, addressed this topic head-on.2 The authors sought to evaluate the accuracy of the UA by analyzing data in a planned secondary analysis of a prospectively collected data set, as part of the Pediatric Emergency Care Applied Research Network (PECARN). We review this publication and present a behind-the-scenes podcast interview with lead author Dr. Leah Tzimenatos.
Podcast with Author Dr. Leah Tzimenatos
What are the test characteristics of the UA for diagnosing UTI in febrile infants ≤60 days old:
- With and without bacteremia?
- When defining UTI as a positive urine culture with either >50,000 or >10,000 colony-forming units (CFU) per mL?
The data was collected from 26 EDs involved in the PECARN collaborative. Patients were included if they were ≤ 60 days of age, had temperature of 38 ℃ or above, and had both urine samples and blood cultures drawn. Urine cultures had to be catheterized or a suprapubic specimen (no bags). Patients were excluded if they had clinical sepsis, prematurity, recent antibiotic use, or significant co-morbid conditions.
- UTI was defined as either ≥ 50,000 CFU/ml of a uropathogen (primary analysis) or 10,000 CFU/ml of a uropathogen (sub-analysis).
- Urine culture was considered negative if it grew no pathogens, >2 pathogens, a known contaminant, or a uropathogen at less than the required CFU/ml.
- Positive UA was defined as positive leukocyte esterase (LE), or positive nitrite, >5 WBC/HPF. LE and nitrite were considered positive if any amount detected, including trace.
- A total of 4,147 infants were included in the data set.
- Overall UTI rate was 7%.
- The sensitivity was 100% and the specificity was 91% for the primary outcome with bacteremia.
- The sensitivity was 94% and the specificity was 91% for the primary outcome without bacteremia.
- For secondary definition (UTI defined as ≥10,000 CFU/ml) the results were similar.
Two interesting results of note:
- Most patients with UTIs were nitrite negative.
- Patients with increasing levels of LE (i.e. 1+ vs 2+ vs 3+) had higher rates of UTI.
The UA is a highly sensitive and specific screening test for UTIs in febrile infants ≤60 days old. It is particularly sensitive in those with associated bacteremia. The UA provides valuable and reliable information to clinicians evaluating the youngest febrile infants for serious bacterial infections.
We overall agree with the authors’ conclusions that the UA is an accurate test in febrile infants ≤60 days old. It is especially sensitive in those patients for whom we are concerned may be at higher risk of complications (those with associated bacteremia). Importantly, it works well as a test to rule-out UTI.