factor VIII measurement (Experimental Factor Ontology identifier EFO_0004630) is is a quantification of factor VIII in serum, Factor 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.[1][2] Defects in this gene results in hemophilia A. Also known as: factor VIII levels.