Haemophilia

Key Information

Appropriate Tests

 

Full blood count, APTT, Prothrombin time, INR.

There is an isolated prolongation of the APTT in severe and moderate haemophilia; the test may not be sufficiently sensitive to detect those with mild haemophilia, with factor VIII or IX levels >30%.

All patients should initially be characterised and registered at a recognised Haemophilia Centre, with monitoring and on-going management organised in consultation with that Centre.

Haemophilia A

Coagulation factor levels - plasma (factor VIII) assay, von Willebrand factor Ag (vWf).

Normal vWf levels serve to differentiate mild haemophilia A from von Willebrand's disease.

  • Factor VIII inhibitor

Develops in approximately 10% of patients: Coagulation factor inhibitors; inhibitor quantitation (Bethesda units) against human and porcine factor VIII if the screening test is positive.

  • Carrier diagnosis

Carrier detection is based on patient and family history; coagulation testing and DNA analysis.

Coagulation factor levels - plasma (factor VIII) assay, von Willebrand factor Ag; the ratio of factor VIII:vWfAg is often reduced (<0.7).

Some carriers have completely normal coagulation results, and the possibility of a carrier state cannot be excluded on these assays. Molecular genetics testing increases the detection rate, but a definitive answer cannot always be obtained.

Carriers with factor VIII levels <50% are at risk of bleeding, ie, they are 'symptomatic carriers'.

Apparent symptomatic carriers need to be distinguished from the von Willebrand's disease Normandy variant.

Haemophilia B (Christmas disease)

Coagulation factor levels - plasma (factor IX) assay.

  • Factor IX inhibitor

Develops in <5% of patients; Coagulation factor inhibitors; inhibitor quantitation if positive.

  • Carrier diagnosis

Coagulation factor levels - plasma (factor IX) assay. Carriers with factor IX levels <50% are at risk of bleeding ie, they are 'symptomatic carriers'.

Some carriers have normal results and the possibility of a carrier state cannot be excluded by factor IX assay. 

Molecular genetics testing increases the detection rate, but a definitive answer cannot always be obtained.

Prenatal diagnosis (haemophilia A and B)

Molecular genetics testing if a DNA marker has previously been identified; chorionic villus biopsy at 8-12 weeks, amniocentesis in the second trimester.

Fetal blood sampling at 18 weeks may be satisfactory for haemophilia A (factor VIII assay) but is less reliable for haemophilia B, as fetal levels of factor IX are normally low.