IL2RA and isolated hyperferritinemia: According to guidelines of the International Histiocyte Society, a diagnosis of HLH requires at least five of the following eight criteria are met: fever, splenomegaly, cytopenias, hypertriglyceridemia or hypofibrinogenemia (or both), hyperferritinemia, elevated soluble interleukin-2 receptor alpha (IL-2Rα), decreased natural killer (NK) cell activity, and hemophagocytosis in bone marrow [4].