Comparative Analysis of Routine Blood Laboratory Tests in Multisystem Inflammatory Syndrome in Children (MIS-C) and Kawasaki Disease Among White and Black Children

This retrospective study evaluated racial differences in age-adjusted laboratory parameters among children with complete Kawasaki Disease (KD) and Multisystem Inflammatory Syndrome in Children (MIS-C). KD cases diagnosed between January 2000-January 2020 using American Heart Association criteria and MIS-C cases diagnosed between January 2021-December 2022 using CDC criteria were identified through the Children's of Alabama electronic medical record. Analyses included Black and White children with complete acute-phase laboratory data for eight routinely obtained parameters: inflammatory markers (Creactive protein [CRP], erythrocyte sedimentation rate [ESR]), hematologic indices (hematocrit, platelet count), renal marker (creatinine), hepatic markers (Aspartate Aminotransferase (AST) and Alanine Transaminase (ALT)), and serum electrolyte (sodium). Laboratory abnormalities were defined using age-specific reference ranges. Logistic regression assessed associations between cumulative laboratory abnormalities and MISC versus KD. The cohort included 243 White KD, 249 Black KD, 43 White MIS-C, and 56 Black MIS-C patients. Compared with KD, MISC patients were older (median age: 10.0 vs. 3.4 years) and was characterized by higher CRP and creatinine and lower ESR, sodium, and platelet counts in both racial groups. Each additional laboratory value below the ageadjusted normal range was associated with increased odds of MISC among White (OR 3.8) and Black (OR 3.4) children, whereas the number of elevated laboratory values was not discriminatory. These findings suggest that MISC and KD are better differentiated by integrated, ageadjusted laboratory patterns of clinically meaningful laboratory abnormalities rather than absolute biomarker levels, supporting patternbased interpretation to improve clinical recognition and risk stratification across diverse pediatric populations.