The criteria described in the RCPHC case definition are persistent fever (duration not defined), inflammation (neutrophilia, lymphopenia, elevated CRP, elevated IL-6 and IL-10 level, etc.)and evidence of single- or multi-organ involvement (such as cardiac, respiratory, renal, gastrointestinal or neurological), along with other clinical and laboratory findings (e.g., elevated troponin, abnormal fibrinogen levels and high D-dimers), an electrocardiogram and imaging results. Here, IL6 is linked to lymphopenia.