Last updated: Friday, 06, August, 2010
|Key Information||Appropriate Tests|
FBC, APTT, PT/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.
Coagulation factors - plasma (factor VIII) assay; von Willebrand factor antigen (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 detection is based on patient and family history; coagulation testing and DNA analysis.
Coagulation factors - plasma (factor VIII) assay, von Willebrand factor antigen; 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 factors - plasma (factor IX) assay.
Factor IX inhibitor
Develops in <5% of patients; coagulation factor inhibitors; inhibitor quantitation if positive.
Coagulation factors - 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.