694 - Performance of Urinary Tract Infection Screening Methods for Febrile Young Children Using Updated American Academy of Pediatrics (AAP) Definitions

Publication Number: 3671.694

Kelly Peterec, Yale-New Haven Children's Hospital, New Haven, CT, United States; Emily Powers, Yale School of Medicine, New Haven, CT, United States; Rakesh D. Mistry, Yale School of Medicine, New Haven, CT, United States

Background: In 2011, the American Academy of Pediatrics (AAP) redefined the criteria for diagnosis of Urinary Tract Infection (UTI) after straight catheterization from >10,000 colony forming units (CFU) of a uropathogen on culture to >50,000 CFU on culture and pyuria.

Objective: To compare the diagnostic performance of screening tests in febrile young children to diagnose UTI using previous culture criteria with the current AAP culture criteria.

Design/Methods: We performed a retrospective review of febrile children aged 2-36 months evaluated in a pediatric emergency department (ED) from 2022-2024 who had a catheterized urinalysis (UA) to screen for UTI. Positive cultures were defined as growth of either >10,000 CFU or the current AAP culture standard of >50,000 CFU of a single uropathogen. If urine culture was not obtained in the ED, patients were considered negative if they did not return with a UTI within one week. We calculated test characteristics for screening methods, including leukocyte esterase (LE), nitrites, and microscopic leukocyturia, in predicting UTI diagnosed by both the previous and the current AAP culture criteria.

Results: A screening UA was obtained in 992 of 8624 eligible children. A urine dipstick was obtained in 990, 604 had a microscopic UA, and 731 had a urine culture. 1 patient without a culture returned for a UTI. Among all screened patients 105 (10.6%) cultures grew >50,000 CFU and an additional 37 cultures grew 10,000-49,999 CFU of a single uropathogen (total 142 [14.3%] >10,000). At a threshold of 50,000 CFU compared to 10,000 CFU, screening tests had higher sensitivity with lower negative likelihood ratio (LR), with optimal threshold of < 5 white blood cells per high powered field and ≤LE of 1+ to rule out UTI (Table). Specificity remained similar, though positive predictive value (PPV) and LR+ was lower for most tests using the 50,000 CFU criteria (Table). The LE threshold for positive culture was 2+, as the LR+ approached 10 regardless of culture positivity criteria (Figure).

Conclusion(s): Given 37 febrile young children grew ≥10,000 CFU of a single uropathogen but did not meet AAP UTI criteria, the new criteria may be overly conservative and result in failure to treat or stoppage of therapy for nearly 1 in 4 possible UTIs. Increasing the threshold for UTI diagnosis from >10,000 to >50,000 CFU increased the ability of screening tests to detect UTI but also increased the likelihood of false positive tests thereby reducing ability to inform treatment. Our data support empiric antibiotic therapy if microscopic UA has >5 wbc/hpf field and a threshold of LE ≥2+.

Test Characteristics for UTI Screening Tests Using Former versus Current AAP Culture Criteria
95% Confidence Interval in Parentheses

Performance of Leukocyte Esterase for UTI Based on Culture Positivity Threshold