Bit · Heme/Onc
Hemophilia A vs B vs vWD
Three bleeding disorders that share the same chief complaint — easy bruising and joint bleeds — but split on PTT, factor levels, and inheritance. The pivot is usually the bleeding pattern (mucocutaneous vs deep).
Mechanism
All three are problems in the clotting cascade or its launchpad:
- Hemophilia A — X-linked recessive deficiency of factor VIII. Intrinsic pathway broken. Deep bleeds — joints, muscles.
- Hemophilia B — X-linked recessive deficiency of factor IX. Same clinical picture as A. (Same pathway, different broken factor.)
- vWD — autosomal dominant deficiency of vWF. vWF does two things: anchors platelets to damaged endothelium and chaperones factor VIII. So you get a platelet-style bleeding pattern plus a mildly low factor VIII.
Differentiator Table
| Hemophilia A | Hemophilia B | vWD | |
| Inheritance | X-linked recessive | X-linked recessive | Autosomal dominant (mostly) |
| Factor missing | VIII | IX | vWF (and ↓ VIII secondarily) |
| PT | Normal | Normal | Normal |
| PTT | ↑ | ↑ | Normal or mildly ↑ |
| Bleeding time / PFA | Normal | Normal | ↑ |
| Bleeding pattern | Deep — joints, muscle | Deep — joints, muscle | Mucocutaneous — epistaxis, menorrhagia, gums |
| Sex affected | Males | Males | Both |
| First-line tx | Recombinant factor VIII (or DDAVP for mild) | Recombinant factor IX | DDAVP (releases stored vWF) |
The Pivot
Two questions decide it:
- Is the bleeding deep (joint/muscle) or mucocutaneous (nose/gums/menses)? Deep → hemophilia. Mucocutaneous → vWD.
- If hemophilia, A or B? Indistinguishable clinically. NBME will give you a factor assay.
Ristocetin cofactor assay is abnormal in vWD — it's the test that proves platelets can't bind vWF.
NBME-Style Stem
A 14-year-old girl is evaluated for heavy menstrual bleeding lasting 9 days and recurrent epistaxis. Her mother and maternal grandmother had similar symptoms. PT is normal, PTT is mildly prolonged, platelet count is normal. Bleeding time is prolonged. Which of the following is the most likely diagnosis?
Concept Anchor
vWF is both a platelet glue and a factor VIII bodyguard — lose it and you bleed like a platelet patient and mildly like a hemophilia patient at the same time.