Urinary Abnormalities Differentiating Kawasaki Disease From Clinically Similar Febrile Illnesses

OBJECTIVE To test the hypothesis that urinary abnormalities differ among Kawasaki disease (KD), multisystem inflammatory syndrome in children (MIS-C), and other pediatric febrile illnesses. METHODS We conducted a cross-sectional analysis of dipstick and automated microscopic urinalyses from participants prospectively evaluated for KD and other causes of fever, for MIS-C, and for urinary tract infection (UTI). We compared urinary leukocyte (WBC) and bacterial counts and levels of bilirubin and urobilinogen among these groups. RESULTS Urinalyses were available for 247 participants with KD, 61 participants with MIS-C, 143 febrile controls (FC), and 45 participants with UTI. Pyuria defined by laboratory reference range (male: >8 WBC/μL; female: >20 WBC/μL) occurred in 73.7%, 66.1%, 47.6%, and 93.3% of the KD, MIS-C, FC, and UTI groups, respectively. High-grade pyuria (≥100 WBC/μL) was common only in KD (26.7%) and UTI (84.4%) and rare in MIS-C (8.9%) and FC (7.0%). Urobilinogen levels of 1.0 mg/dL or more (39.3% of KD, 36.7% of MIS-C, 24.6% of FC) were rare in UTI (2.2%), whereas bilirubin levels of 1+ or greater (15.0% of KD, 35.0% of MIS-C) were rare in both FC and UTI (2.8% and 2.2%, respectively). CONCLUSIONS Pyuria commonly exceeded reference range in all groups. However, high-grade pyuria was common only in KD and UTI and can help differentiate these illnesses from MIS-C and FCs. Elevations of urinary urobilinogen and bilirubin levels were common in KD and MIS-C and distinguish KD with pyuria from UTI. These urinary data will inform future work in clinical decision-making and support tools.