(e) Hemophagocytosis in bone marrow or spleen or lymph nodes, no evidence of malignancy
(f) Serum ferritin ≥ 500 µg/L (i.e., 500 ng/ml)
(g) Low or absent NK cell activity (according to local laboratory reference)
(h) Increased serum sIL2Rα (according to local laboratory reference)
If hemophagocytic activity is not proven at the time of presentation, further search for hemophagocytic activity is encouraged. If the bone marrow specimen is not conclusive, material may be obtained from other organs. Table 1 is copied from Henter et al. [17].