IL2RA and isolated hyperferritinemia: A diagnosis of HLH is made by meeting at least five of the eight HLH-2004 diagnostic criteria, which include fever, splenomegaly, cytopenia affecting >2 of 3 peripheral blood lineages (hemoglobin <90 g/L, platelets <100 × 10^9/L, neutrophils <1.0 × 10^9/L), hypertriglyceridemia (fasting triglycerides >3.0 mmol/L) and/or hypofibrinogenemia (fibrinogen <1.5 g/L), hemophagocytosis (in bone marrow, spleen, or lymph nodes), hyperferritinemia (>500 μg/L), elevated soluble CD25 (>2400 U/mL), and decreased NK cell activity [1].