Molecular diagnosis of hemophagocytic lymphohistiocytosis (HLH) or X-linked lymphoproliferative syndrome (XLP).

Or at least 3 of 4:

• Fever

• Splenomegaly

• Cytopenias (minimum 2 cell lines reduced)

• Hepatitis

And at least 1 of 4:

• Hemophagocytosis

• ↑ Ferritin

• ↑ sIL2Rα (age based)

• Absent or very decreased NK function

Other results supportive of HLH diagnosis:

• Hypertriglyceridemia

• Hypofibrinogenemia

• Hyponatremia