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Table 1 Diagnostic criteria for HLH used in HLH-2004 trial [9]

From: Macrophage activation syndrome in MDA5 antibody-positive dermatomyositis and COVID-19 infection

A

Molecular diagnosis consistent with HLH associated mutations (PRF1, UNC13D, STX11, STXBP2, Rab27A, SHD1A, BIRC4, LYST, ITK, SLC7A7, XMEN, HPS)

B

Or 5 of 8 criteria listed below

1

Fever ≥  38.5 °C

2

Splenomegaly

3

Peripheral blood cytopenia, with at least two of the following: hemoglobin < 9 g/dL (for infants < 4 weeks, hemoglobin < 10 g/dL); platelets < 100,000/microL; absolute neutrophil count < 1000/microL

4

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

5

Hemophagocytosis in bone marrow, spleen, lymph node, or liver

6

Low or absent NK cell activity

7

Ferritin > 500 ng/mL

8

Elevated soluble CD25 (soluble IL-2 receptor alpha [sIL-2R]) two standard deviations