Hematology

Hemophilia A

X-linked recessive deficiency of coagulation factor VIII causing spontaneous and traumatic bleeding, especially haemarthrosis; severity by baseline factor level.

Last reviewed 20 Jun 2026 - MedicoMedics editorial team

Coagulation cascade factor VIII deficiency

Pathophysiology

F8 gene mutation on Xq28 (inversion in ~45% severe cases); factor VIII acts as cofactor for factor IXa in intrinsic pathway.

Sources: WFH Guidelines 2020; Valrox NEJM 2022;386:1013

Presentation

Severe (<1%): spontaneous haemarthrosis, muscle haematomas, intracranial haemorrhage; moderate (1-5%): bleeding with trauma/surgery; mild (>5%): surgical/dental bleeding.

Diagnosis

Prolonged aPTT corrected by mixing study, normal PT and platelets; factor VIII activity assay. Family history in ~70%.

Management

Prophylactic recombinant factor VIII (extended half-life products) or emicizumab (bispecific mimicking FVIII). Acute bleed: replacement to 50-100% target. Gene therapy (valoctocogene roxaparvovec) approved for adults.

Sample USMLE-style MCQs

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Question 1

A 3-year-old boy has recurrent knee haemarthrosis. PT normal, aPTT prolonged. Family history maternal uncle. Diagnosis?

Question 2

Which agent provides once-weekly subcutaneous prophylaxis without factor VIII?

Question 3

Which is contraindicated as monotherapy in severe hemophilia A?

Question 4

Management of acute intracranial haemorrhage in severe hemophilia A?

Question 5

Curative option approved recently?

References

Primary guidelines and peer-reviewed sources used for this entry. Reviewed 20 Jun 2026 by MedicoMedics editorial team.

Frequently asked

Distinguish A from B?

Both prolong aPTT; factor VIII (A) or IX (B) assays distinguish.

What is emicizumab?

Bispecific antibody bridging factor IXa to factor X; subcutaneous prophylaxis.

Inhibitor development?

Alloantibodies to FVIII in ~30% - use bypassing agents (aPCC, rFVIIa) or emicizumab.

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