Factor VIII Deficient plasma is drawn from a human donor with a congenital deficiency. Human plasma from donor with FVIII Deficiency. Confirmed normal level of von Willebrand factor activity. Substrate quality. <1% FVIII Activity by one stage clotting assay. No buffers or perservatives added. When doing factor assays, it is critical to have only a single factor deficient in the substrate plasma (monospecificity).