Adults
Macrophage activation syndrome / HLH (adult)
Persistent fever with cytopenias and a very high or rising ferritin in Still's disease, lupus, infection or cancer.
What to look for
- Unremitting fever with new or worsening cytopenias
- Very high or rapidly rising ferritin (often above 5,000–10,000 ng/mL), raised AST/ALT, LDH and triglycerides
- Falling fibrinogen and ESR despite a rising CRP. This mismatch is a classic warning sign.
- Hepatosplenomegaly, coagulopathy, confusion or multiorgan dysfunction
What to do
- Send to the emergency department. Involve rheumatology and hematology the same day.
- Check CBC, ferritin, fibrinogen, triglycerides, liver tests, LDH, coagulation studies and blood cultures. Look for an infectious or malignant trigger.
Good to know
- Emapalumab was FDA-approved in June 2025 for HLH/MAS in known or suspected Still's disease (including systemic JIA), in adults and children, with an inadequate response or intolerance to glucocorticoids, or recurrent MAS.
About this urgency level
Call rheumatology directly. Many of these need the emergency department or admission, and treatment often starts before the specialist visit.
Timeframes are typical targets. Local pathways, capacity and clinical judgment come first.