Patients who exhibit five or more of the following findings meet the diagnostic criteria for hemophagocytic lymphohistiocytosis (HLH).

Clinical findings

  • Fever ≥ 38.5ºC
  • Splenomegaly on examination or imaging

Laboratory findings

  • Ferritin > 500 ng/mL
  • Cytopenias involving at least two cell lines
    • Hemoglobin < 9 g/dL (SI unit: 90 g/L)
    • Neutrophil < 1,000 per mm3 (SI unit: < 1.0 x 109/L)
    • Platelet count < 100,000 per mm3 (SI unit: < 100 x 109/L)
  • Elevated fasting triglycerides > 265 mg/dL
  • Low fibrinogen (hypofibrinogenemia) < 150 mg/dL
  • Presence of hemophagocytosis on biopsy
  • Reduced or absent NK cell activity
  • Elevated CD25/IL-2 receptor alpha activity (especially if ≥ 2 standard deviations above normal)