IL2RA and Splenomegaly: The diagnostic criteria are determined by the HLH-2004 trial, which requires the presence of at least five of the eight following features: fever ≥38.5°C, splenomegaly, peripheral blood cytopenia, hypertriglyceridemia and/or hypofibrinogenemia, hemophagocytosis in bone marrow, spleen, lymph node, or liver, low or absent natural killer (NK) cell activity, ferritin >500 ng/mL, elevated soluble CD25 (soluble IL-2 receptor alpha) two standard deviations above age-adjusted laboratory-specific norms [10].