Diagnostic test accuracy of dipstick urinalysis in clean catch urine for urinary tract infection in febrile infants presenting to emergency departments: a post-hoc analysis of the FIDO study.

Background: Studies where urine is typically obtained via invasive methods, show dipstick urinalysis can accurately screen for urinary tract infection (UTI) in febrile infants under 90 days old. However, evidence is limited in settings where clean catch urine collection is standard practice. This study assessed the accuracy of dipstick for UTI in a prospective cohort of febrile infants presenting to UK and Ireland emergency departments, where clean catch is the predominant urine collection method. Methods: Post-hoc analysis of the Febrile Infant Diagnostic Assessment and Outcome study, a prospective multicentre observational cohort study. Febrile infants ≤90 days old were recruited from 35 Paediatric Emergency Research in the UK and Ireland (PERUKI) sites (NCT05259683) between 6th July 2022 and the 31st August 2023. Accuracy of dipstick urinalysis testing for detecting UTI was reported with sensitivity, specificity and predictive values. Findings: In this multicentre prospective study of 1821 febrile infants ≤90 days, point-of-care dipstick urinalysis was performed in 57.1% of cases. Diagnostic accuracy varied significantly by age, sex, and method of dipstick assessment. Sensitivity was lowest in neonates (≤28 days; 53.3%) and if dipsticks were user-inspected (57.1%), highlighting limitations in these subgroups. In contrast, automated dipstick testing in infants >28 days achieved high sensitivity (87.5%) and moderate specificity (73.4%) at a cut-off of ≥trace leukocytes and/or ≥trace nitrites. Specificity was notably lower in female infants (60.3%) than males (85.0%), likely due to higher contamination rates in clean catch samples. Interpretation: Automated dipstick urinalysis offers a reliable method for excluding UTI in infants >28 days and can guide selective urine culture use when clean catch urine sampling is used. However, dipstick testing of samples obtained by clean catch should not be used to rule out UTI in neonates or when relying on manual interpretation due to poor sensitivity. Funding: Royal College of Emergency Medicine Doctoral Fellowship (RCEM 02/03/2021), the funders played no part in study conception or design.