An 18-month-old boy presents with recurrent swelling and restricted movement of the right knee. His father had a similar problem requiring factor replacement. PT is normal, aPTT is markedly prolonged, and bleeding time is normal. Which finding would best classify the severity of his disease?

• A Factor VIII activity as a percentage of normal plasma level ✓
• B Absolute aPTT value in seconds
• C Factor IX antigen level
• D Platelet count

Explanation

Hemophilia A severity is defined by residual factor VIII activity: less than 1 percent is severe with spontaneous hemarthroses, 1 to 5 percent moderate, and above 5 percent mild disease. The father-son history fits X-linked inheritance. The absolute aPTT does not grade severity because it plateaus once factor levels fall below roughly 30 percent. Factor VIII activity below 1 percent also kills the hemophilia B distractor, which requires factor IX assay for confirmation.

Reference: Nelson Textbook of Pediatrics, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.