A 6-year-old boy with established systemic juvenile idiopathic arthritis, previously controlled on therapy, develops 3 days of fever with hepatosplenomegaly and lymphadenopathy. Investigations show a platelet count falling from 320 to 90 x 10^9/L, WBC 3.2 x 10^9/L, AST 180 U/L, LDH 900 U/L, and serum ferritin 14,000 ng/mL. Which single laboratory profile best confirms the complication?

• A Serum ferritin greater than 10,000 ng/mL together with rapidly falling platelet and white cell counts ✓
• B Progressive rise in ESR with sustained neutrophilic leukocytosis
• C Low serum ferritin with a Coombs negative hemolytic anemia
• D Isolated elevation of alkaline phosphatase with normal transaminases

Explanation

Macrophage activation syndrome is a life threatening hyperinflammatory complication of systemic JIA. Its hallmark is extreme hyperferritinemia (often above 10,000 ng/mL) accompanied by cytopenias from hemophagocytosis, high LDH, and high transaminases. The tempting distractor B is wrong because in MAS the ESR paradoxically falls as fibrinogen drops, unlike a simple disease flare where ESR rises.

Reference: Nelson Textbook of Pediatrics, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.