Investigations

The following results occur in Haemophilia A and Haemophilia B:

• activated partial thromboplastin time (APTT); prolongation depends on the severity of the factor deficiency. Prolonged APTT plus prolonged bleeding suggests von Willebrand's disease
• factor VIII clotting assay - low levels in Haemophilia A
• factor IX clotting assay - low levels in Haemophilia B
• note that in severe cases of Haemophilia B whole blood coagulation time is increased (1)

Other investigations:

• normal tests in Haemophilia A and Haemophilia B include:
  • prothrombin time (PT)
  • bleeding time
  • normal von Willebrand factor
• Other investigations include:
  • DNA probes - genes for Factor VIII and Factor IX have been cloned and characterised.
  • pedigree analysis - may diagnose female carriers with certainty in some situations - for example all daughters of a known haemophiliac male are obligate carriers

Reference:

1. Hoffbrand AV, Pettitt JE (1999). Essential Haematology. Blackwell Scientific Publications, Oxford.