Table 1.

Criteria for MIS-C diagnosis.

Agency	World Health Organization (WHO)23	Centers for Disease Control and Prevention (CDC), USA	Royal College of Paediatrics and Child Health (RCPCH), UK22	Proposed uniform definition
Age	0–19 years	<21 years	Child (age not specified)	<21 years
Fever	≥3 days	Fever ≥38.0 °C for ≥24 h, or report of subjective fever lasting ≥24 h	Persistent fever >38.5 °C	Fever ≥38.0 °C for ≥3 days, or report of subjective fever lasting ≥3 days
AND	At least two of the following	≥2 organ system involvement		≥2 organ involvement with specified signs
Clinical features	1 Rash or bilateral non-purulent conjunctivitis or mucocutaneous inflammation signs (oral, hands, or feet) 2 Hypotension or shock 3 Features of myocardial dysfunction, pericarditis, valvulitis, or coronary abnormalities (including ECHO findings or elevated Troponin/NT-proBNP) 4 Evidence of coagulopathy (by PT, PTT, elevated D-dimers) 5 Acute gastrointestinal problems (diarrhea, vomiting, or abdominal pain)	Evidence of clinically severe illness requiring hospitalization, with multisystem (≥2) organ involvement (cardiac, renal, respiratory, hematologic, gastrointestinal, dermatologic, or neurological)	Evidence of single or multiorgan dysfunction (shock, cardiac, respiratory, renal, gastrointestinal, or neurological disorder) Most have oxygen requirement and hypotension Some have abdominal pain, confusion, conjunctivitis, cough, diarrhea, headache, lymphadenopathy, mucus membrane changes, neck swelling, rash, resp symptoms, sore throat, swollen hands and feet, syncope, and vomiting	Cardiac: hypotension or shock, myocardial dysfunction, pericarditis, valvulitis, or coronary abnormalities, pericardial effusion (including ECHO findings or elevated Troponin/NT-proBNP) Gastrointestinal: diarrhea, vomiting, or abdominal pain Mucocutaneous: rash or bilateral non-purulent conjunctivitis, sore throat or mucocutaneous inflammation signs (oral, hands or feet) Hematologic: lymphadenopathy, thrombocytopenia, lymphopenia, evidence of coagulopathy (by PT, PTT, elevated D-dimers) Renal: acute kidney injury Respiratory distress, cough Neurological: confusion, headache, seizures
AND
Markers of inflammation	Elevated markers of inflammation such as ESR, C-reactive protein, or procalcitonin	One or more of the following: an elevated C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), fibrinogen, procalcitonin, D-dimer, ferritin, lactic acid dehydrogenase (LDH), or interleukin 6 (IL-6), elevated neutrophils, reduced lymphocytes, and low albumin	Inflammation (neutrophilia, elevated CRP, and lymphopenia) Abnormal fibrinogen, elevated CRP, D-dimers or ferritin, hypoalbuminemia, lymphopenia, neutrophilia in most; normal neutrophils in some	One or more of the following (based on age-appropriate cut-offs): an elevated C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), fibrinogen, procalcitonin, D-dimer, ferritin, lactic acid dehydrogenase (LDH), or interleukin 6 (IL-6), elevated neutrophils, reduced lymphocytes, and low albumin
AND
Absence of other etiology	No other obvious microbial cause of inflammation, including bacterial sepsis, staphylococcal or streptococcal shock syndromes	No alternative plausible diagnoses	Exclusion of any other microbial cause, including bacterial sepsis, staphylococcal or streptococcal shock syndromes, infections associated with myocarditis such as enterovirus	No alternative plausible diagnoses
AND
Evidence of COVID-19	Evidence of COVID-19 (RT-PCR, antigen test, or serology positive), or likely contact with patients with COVID-19	Positive for current or recent SARS-CoV-2 infection by RT-PCR, serology, or antigen test; or exposure to a suspected or confirmed COVID-19 case within the 4 weeks prior to the onset of symptoms	SARS-CoV-2 PCR testing may be positive or negative	Positive for current or recent SARS-CoV-2 infection by RT-PCR, serology (not explained by prior immunization), or antigen test; or recent exposure to a suspected or confirmed COVID-19 case