The majority of patients with hemophilia have a known family history
of the condition. However, about one-third of cases occur in the absence
of a known family history. Most of these cases without a family history
arise due to a spontaneous mutation in the affected gene. Other cases
may be due to the affected gene being passed through a long line of
female carriers.
If there is no known family history of hemophilia, a series of blood
tests can identify which part or protein factor of the blood clotting
mechanism is defective if an individual has abnormal bleeding episodes.
The platelet (a blood particle essential for the clotting process)
count should be measured as well as two indices of blood clotting, the
prothrombin time (PT) and activated partial thromboplastin time (aPTT). A
normal platelet count, normal PT, and a prolonged aPTT are
characteristic of hemophilia A and hemophilia B. Specific tests for the
blood clotting factors can then be performed to measure factor VII or
factor IX levels and confirm the diagnosis.
Genetic testing to identify and characterize the specific mutations
responsible for hemophilia is also available in specialized
laboratories.
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