FRCPath Haem Part 1 MCQs-Haemostasis 469

A 76-year-old woman presents with spontaneous extensive bruising, painful swelling of the right thigh, and persistent epistaxis. She has a history of rheumatoid arthritis and hypertension but no previous bleeding disorder. Examination reveals large ecchymoses over the limbs and a tense right thigh suggestive of an intramuscular haematoma.

Initial laboratory investigations show:

Test	Result
Hb	84 g/L
Platelets	295 ×10⁹/L
APTT	96 seconds (reference 24–36)
Mixing study	Fails to correct immediately and after incubation
FVIII activity	<1 IU/dL
Bethesda inhibitor titre	82 BU

She receives recombinant porcine FVIII initially, together with prednisolone and rituximab for inhibitor eradication.

The multidisciplinary team decides to commence emicizumab as prophylaxis while continuing immunosuppressive therapy.

Two weeks later she develops mild calf pain after prolonged immobility. Doppler ultrasound confirms a distal deep vein thrombosis. Laboratory testing shows:

• APTT: 24 seconds

• One-stage FVIII assay: 240 IU/dL

• Chromogenic bovine FVIII assay: 5 IU/dL

• D-dimer: Elevated

The haematology registrar is concerned that the laboratory findings appear contradictory and wonders whether emicizumab should be discontinued because of thrombosis.

Which ONE of the following statements is MOST accurate?

A. The normal APTT and markedly elevated one-stage FVIII assay indicate excessive FVIII replacement from emicizumab

B. Emicizumab neutralises the FVIII inhibitor, so the Bethesda inhibitor titre becomes unreliable after treatment begins.

C. The elevated one-stage FVIII assay is an artefact caused by emicizumab

D. Emicizumab therapy proves the drug is contraindicated in acquired haemophilia A and should never be restarted.

E. APTT remains the preferred assay for monitoring emicizumab dose adjustment because it reflects the drug's pharmacodynamic activity.