Hemophagocytic Lymphohistiocytosis

The diagnosis of HLH is established by fulfilling one of the following 2 criteria:

• 1) A molecular diagnosis consistent with HLH (e.g., PRF mutations, SAP mutations)

2) Presence of 5 of the following 8 symptoms, signs, or laboratory abnormalities:

• a) Fever
• b) Splenomegaly
• c) Cytopenia (affecting ≥2 cell lineages; hemoglobin ≤9 g/dL [or ≤10 g/dL for infants <4 wk old], platelets <100,000/µL, neutrophils <1,000/µL)
• d) Hypertriglyceridemia (≥265 mg/dL) and/or hypofibrinogenemia (≤150 mg/dL)
• e) Hemophagocytosis in the bone marrow, spleen, or lymph nodes without evidence of malignancy
• f) Low or absent natural killer cell cytotoxicity
• g) Hyperferritinemia (≥500 ng/mL)
• h) Elevated soluble CD25 (interleukin-2Rα chain; ≥2,400 U/mL)