Normative Laboratory Value Ranges in Pediatric Patients Who Underwent Evaluation for MIS‐C

Background and Objectives Diagnosis of multisystem inflammatory syndrome in children (MIS‐C) is challenging due to symptom overlap with other common conditions. The primary objective of this multicenter study was to establish normative laboratory values in MIS‐C patients and compare to patients evaluated for MIS‐C who had other final diagnoses. Methods Five hospitals reviewed records of a cohort of patients 6 months to 18 years old who were evaluated for MIS‐C between March 31 st 2020 and February 1 st 2022. Patient demographics, clinical presentation, and laboratory values were compared in patients with a final diagnosis of MIS‐C versus all other conditions. Patients’ final diagnoses and laboratory values for each diagnosis were reported. Results Of the 1319 patients that were evaluated for MIS‐C at presentation, 293 (22.2%) received a final diagnosis of MIS‐C. MIS‐C patients had statistically significant differences in laboratory values including D‐dimer, ferritin, fibrinogen, troponin, and brain natriuretic peptide when compared to patients evaluated for MIS‐C but subsequently diagnosed with other conditions. The most common non‐MIS‐C diagnoses within this cohort were viral illnesses (26.7%), acute COVID‐19 (12.0%), pyelonephritis (6.4%), fever of unknown origin (4.9%), pneumonia (4.7%), gastroenteritis (4.7%), Kawasaki disease (3.7%), other bacterial infections, (3.1%), rheumatologic conditions (3.1%), and sepsis (2.8%). Conclusions Many patients who underwent laboratory evaluation for MIS‐C during the COVID‐19 pandemic received a final diagnosis other than MIS‐C. These data may aid pediatricians in differentiating between MIS‐C and other febrile conditions as well as reduce unnecessary testing.