Hemophilia

Boys born to women who are known carriers for hemophilia A or B have a 50% chance of having inherited hemophilia 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 hemophilia A or B are obligate carriers. Girls born to women who are known carriers for hemophilia 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 noncarriers (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:​[34]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 hemophilia A or B

• Affected male relatives

• Female relatives at risk of being carriers.