Haemophilia

Boys born to women who are known carriers for haemophilia A or B have a 50% chance of having inherited haemophilia A or B. Therefore, these boys should be tested at birth, by sending cord blood for activated partial thromboplastin time and factor VIII and/or factor IX assay. Mild factor IX deficiency may be difficult to diagnose because of the physiological decrease in vitamin K-dependent clotting factors at birth.

Girls born to men with haemophilia A or B are obligate carriers. Girls born to women who are known carriers for haemophilia A or B have a 50% chance of being carriers themselves. These girls may be tested with factor VIII or factor IX assays. On average, carriers have 50% of the normal factor VIII or factor IX levels. However, factor VIII and factor IX levels in carriers frequently overlap with the levels of non-carriers (such that normal factor VIII or IX levels do not exclude being a carrier in at-risk females). Hence, DNA mutation analysis is the most accurate test for carrier detection.[64]Brown DL. Congenital bleeding disorders. Curr Probl Pediatr Adolesc Health Care. 2005 Feb;35(2):38-62. http://www.ncbi.nlm.nih.gov/pubmed/15692557?tool=bestpractice.com

Candidates for genetic testing include:​[35]National Hemophilia Foundation Medical and Scientific Advisory Council (MASAC). MASAC Document 273 - Recommendations on Genotyping for Persons with Hemophilia. Jul 2022 [internet publication]. https://www.hemophilia.org/healthcare-professionals/guidelines-on-care/masac-documents/masac-document-273-recommendations-on-genotyping-for-persons-with-hemophilia

• Patients with a diagnosis of haemophilia A or B

• Affected male relatives

• Female relatives at risk of being carriers.