Table 2 Diagnostic criteria of HLH—2004

1. Fever of 38.5 °C or more

2. Splenomegaly

3. Cytopenia (affecting at least two cell lineages in the peripheral blood)

∙ Hemoglobin < 9 g/dL

∙ Platelets < 100,000/μL

∙ Absolute neutrophil count < 1000/μL

4. Hypertriglyceridemia (fasting triglycerides > 265 mg/dL) and/or hypofibrinogenemia (fibrinogen < 150 mg/dL)

5. Hemophagocytosis in bone marrow, spleen, lymph nodes, or liver

6. Low or absent natural-killer-cell activity

7. Ferritin > 500 ng/mL

8. Increased soluble CD25 concentration (alpha chain of soluble interleukin-2 receptor)

The diagnosis of HLH requires the presence of five of the above criteria