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Carrier diagnosis

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:
  • all daughters of a father with haemophilia;
  • mothers of one son with haemophilia and who have at least one other family member with haemophilia (a brother, maternal grandfather, uncle, nephew, or cousin);
  • mothers of one son with haemophilia and who have a family member who is a known carrier of the haemophilia gene (a mother, sister, maternal grandmother, aunt, niece, or cousin);
  • mothers of two or more sons with haemophilia.
  • all daughters of a carrier;
  • mothers of one son with haemophilia but who do not have any other family members who have haemophilia (or are carriers);
  • sisters, mothers, maternal grandmothers, aunts, nieces, and female cousins of carriers.

Laboratory tests

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.