TABLE 1

Diagnostic Criteria for HLH4

Fulfillment of 5 of the 8 criteria listed below:
1. Fever
2. Splenomegaly
3. Cytopenias (affecting at least 2 of 3 lineages in the peripheral blood):
• Hemoglobin <9 g/100 mL (in infants <4 wk: hemoglobin <10 g/100 mL)
• Platelets <100 × 109/L
• Neutrophils <1 × 109/L
4. Hypertriglyceridemia (fasting, ≥265 mg/100 mL) and/or hypofibrinogenemia (≤150 mg/100 mL)
5. Hemophagocytosis in bone marrow, spleen, or lymph nodes
6. Low or absent natural killer cell activity
7. Ferritin ≥500 ng/mL
8. Soluble CD25 (soluble interleukin-2 receptor) >2400 U/mL (or per local reference laboratory)