Haemophilia A (factor VIII deficiency) and haemophilia B (factor IX deficiency) are sex-linked inherited bleeding disorders.
When haemophilia is passed along a family, the type and severity of haemophilia is always the same in the male with haemophilia. However, clotting factor levels in carriers are independent of the severity of the haemophilia in males and can vary from person to person because of lyonization. A carrier of a mild form of haemophilia can have the same factor levels as a carrier of the severe form of haemophilia. Within a family factor levels in related carriers can be very different, ranging from very low to normal.
Those with clotting factor levels from 0.05 iu/ml – 0.4 iu/ml are diagnosed as having mild haemophilia, 0.01 iu/ml – 0.05 iu/ml as moderate haemophilia and less than 0.01 iu/ml as severe haemophilia. Females may experience the same problems as males with the same factor levels. The majority of carriers have clotting factor level between 0.4 iu/ml and 0.7 iu/ml and do not bleed. A carrier who has a factor level less than o.4iu/ml can be considered to have mild haemophilia or to be a “symptomatic carrier”. All carriers (possible and obligate) should have factor VIII or IX level checked because of the increased risk of bleeding in carriers with low factor levels.
Recent studies have shown that women with clotting factor levels as high as 0.6iu/ml can have abnormal bleeding problems, including, but not restricted to gynaecological and obstetric bleeding. Up to 57% of carriers do have gynaecological problems related to excessive menstrual bleeding which can vary from mild to severe.
Symptomatic carriers are those with an increased bleeding tendency due to reduced clotting factor. The risk of bleeding is highest in those with the lowest clotting factor levels. Some of these bleeding symptoms include:
- Easy bruising.
- Prolonged bleeding from minor wounds.
- Bleeding from the nose (epistaxis).
- Prolonged bleeding after tooth extraction or surgery.
- Prolonged bleeding after trauma.
- Heavier and more prolonged bleeding during periods (menorrhagia)
- Increased risk of bleeding following delivery ( post partum haemorrhage)
Factor VIII or factor IX assay: This measures the amount of factor VIII or factor IX in the blood. It is important to know the factor VIII or IX level early in life as girls with low factor levels are at increased risk of bleeding. A girl with a normal factor level may still be a carrier of factor VIII or IX deficiency. Factor VIII level can be affected by hormone levels (pregnancy, contraceptive pills, breast-feeding), by physical and mental stress and exercise. Factor IX levels are not affected by hormones.
Genetic analysis to determine carrier status
There are a number of genetic tests that can be done to determine carrier status. These tests are complex. Results are more reliable if DNA from a family member with haemophilia is also available.
Genetic testing in childhood versus genetic testing in adulthood
In Ireland, the policy is that a possible carrier must be old enough to understand the implications of the test results before genetic testing is carried out. This is usually after 16 years of age. The sooner a girl is tested after this age, the more time she has to come to terms with being a carrier. It also prepares her for eventual decisions about pregnancy and childbirth.