Patients with an HLH-associated gene defect and/or at least five of the following eight criteria can be diagnosed with HLH: fever, low or absent natural killer cell function, cytopenias, splenomegaly, increased triglycerides or low fibrinogen, high ferritin, hemophagocytosis, and elevated soluble CD25 (interleukin 2 receptor alpha (IL2Rα)) [67]. This evidence concerns the gene IL2RA and Splenomegaly.