IL2RA and isolated hyperferritinemia: HLH diagnosis requires five out of nine diagnostic criteria (“HScore”): fever; splenomegaly; cytopenias affecting two or three lineages (hemoglobin < 9 g/dL, platelets < 100,000/μL, and neutrophils < 1000/μL); hypertriglyceridemia and/or hypofibrinogenemia; hemophagocytosis in the bone marrow, spleen, lymph nodes, or liver; hyperferritinemia; low or absent NK cell activity; and increased soluble CD25 (IL‐2r) concentration (> 2400 U/mL) [3, 6].