Table 1 Diagnostic criteria for HLH used in the HLH-2004 trial

Five of the eight criteria listed below should be fulfilled

Fever ≥38.5 °C

Splenomegaly

Cytopenias (affecting at least 2 of 3 lineages in the peripheral blood)

 Hemoglobin <9 g/dL (in infants <4 weeks: hemoglobin <10 g/dL)

 Platelets <100 × 10³/mL

 Neutrophils <1 × 10³/mL

Hypertriglyceridemia (fasting, >265 mg/dL) and/or hypofibrinogenemia (<150 mg/dL)

Hemophagocytosis in bone marrow, spleen, lymph nodes, or liver^a

Ferritin >500 ng/mL

Elevated sCD25 (α-chain of sIL-2 receptor)

Low or absent NK-cell activity