Mixing Studies and Factor Assays

George is attending the International Society for Laboratory Hematology in Chicago, where he was presented a follow-up mixing studies question that was provoked by excellent discussions led by Drs. Mary Robinson and Dorothy Adcock of Esoterix Coagulation. The questioner performs a 1:1 mixing study using NP, and if it corrects, follows up with a mixing study using FVIII and FIX-deficient plasmas, chekcing for the most likely congenital deficiencies. The questioner notices that sometimes the factor IX deficient plasma may partially correct despite absence of FIX. George suggested there may be some residual FIX in the reagent plasma. Do any of our subscribers have another suggestion?