*Supportive criteria include neurologic symptoms, cerebrospinal fluid pleocytosis, conjugated hyperbilirubinemia and transaminitis, hypoalbuminemia, hyponatremia, elevated D-dimers, and lactate dehydrogenase (see text for details). The absence of hemophagocytosis in the BM does not exclude a diagnosis of HLH.

†New data show normal variation by age. Level should be compared with age-related norms.

(Adapted with permission from Henter et al²⁰ .)