Factor VIII participates in blood coagulation; it is a cofactor for factor IXa which, in the presence of Ca 2+ and phospholipids forms a complex that converts factor X to the activated form Xa.The factor VIII gene produces two alternatively spliced transcripts.actor VIII (FVIII) is an essential blood-clotting protein, also known as anti-hemophilic factor (AHF). In humans, factor VIII is encoded by the F8 gene.