21/10/2026
Have you heard of ‘haemophilia C’? Today this bleeding disorder is known as factor XI deficiency.
Factor XI (11) deficiency is a rare clotting factor deficiency. Unlike haemophilia – also known as factor VIII (8) or factor IX (9) deficiency - factor XI deficiency rarely causes joint or muscle bleeding. It is estimated to affect one in 100,000 people, and in Australia is the third most common bleeding disorder to affect women after von Willebrand disease (VWD) and haemophilia.