Box 1.

HLH-2004 diagnostic criteria3

Molecular diagnosis known to cause HLH 
or
 meeting 5 out of the following 8 criteria
  • fever

  • splenomegaly

  • cytopenias in peripheral blood:

    • haemoglobin <90 g/L

    • platelets <100×109/L

    • neutrophils <1×109/L

  • haemophagocytosis in bone marrow, lymph nodes or spleen

  • low or absent natural killer cell activity

  • ferritin >500 ng/mL

  • raised soluble CD25 (IL-2 receptor)

  • fasting hypertriglyceridaemia (>3 mmol/L) or hypofibrinogenaemia

  • HLH= haemophagocytic lymphohistiocytosis