There are two types of carriers: obligate carriers and possible carriers. Obligate carriers necessarily have the haemophilia gene, which they inherit from their father. Obligate carriers can be identified by getting a detailed family history (known as a pedigree).
|Obligate carriers are:||Possible carriers are:|
Two kinds of laboratory tests can be performed for carriers of haemophilia:
Factor assays measure the amount of clotting factor in a person’s blood. While this information is useful, some carriers will have normal clotting factor levels. Therefore, this test has the potential to provide falsely reassuring or incorrect information to women who may indeed be carriers.
Genetic tests such as mutation analysis look directly for the altered gene that’s responsible for haemophilia. This is the only way to be absolutely sure that a woman is a carrier. Information obtained from these tests is also more revealing for other family members. However, genetic tests can be costly and may not be available in all centres.