BOF: Clotting (Haemophilia)

A twenty-six year old woman presents with easy bruising, menorrhagia, and recurrent epistaxis. This has been present as long as she can remember but she is now finding it more troublesome. Her father and paternal aunt had similar problems but were never treated. Von Willebrand’s disease (VWD) is suspected: which ONE of the following blood parameters is MOST LIKELY to be normal if this diagnosis is confirmed?

a) Activated partial thromboplastin time and prothrombin time are abnormal in >70% of cases.

b) Ferritin

c) Bio-active membrane aperture closure platelet function analyser (e.g. PFA-100) closure time

d) Platelet count

e) Prothrombin time

The answer is:

Prothrombin time

Explanation:

VWF acts as a carrier for factor VIII and as such APTT may be prolonged through reduction of FVIII levels, particularly in the rare 2N VWD. It is however frequently normal. 2B VWD leads to a reduced platelet count through increased affinity for the GPIb and consumption. Ferritin may be reduced due to menorrhagia and gastro-intestinal blood loss with consequent iron deficiency. The Bio-active membrane aperture closure platelet function analyser (e.g. PFA-100) closure time assess platelet aggregation through exposure of whole blood to collagen and a platelet activator (ADP or Adrenaline) under high shear stress conditions. It is more sensitive than the bleeding time in detecting VWD. Prothrombin time will not be affected by VWD.

Reference:

Laffan M, Brown SA, Collins PW et al. The diagnosis of von Willebrand disease: a guideline from the UK Haemophilia Centre Doctors' Organization. Haemophilia 2004 May;10(3):199-217.