Treatment algorithm for aHLH. Focus of aHLH-mangement is detecting and treating the trigger disease. HLH-specific treatment (VP-16, CSA, IVIG) is required in severe HLH prior to prevent irreversible organ damage (liver, kidney, or respiratory failure). Hourly/daily reassessment is mandatory. Close contact to HLH-reference centre is recommended; *Indicates treatment with CAR T cells or T-cell engaging antibodies; §, off label; αCD20, Rituximab; αIL1R, Anakinra; αIL6R, Tocilizumab; MPPT, methylprednisolone pulsed therapy; Pt, patient; and VP-16, etoposide.