Discrepancy between One‐stage and Two‐stage Assay of Factor VIII:C

Abstract
Summary. Two methods (one‐stage and two‐stage) are commonly used for the assay of factor VIII clotting activity (VIII:C). We present collected data from seven separate studies of VIII:C assay which show that these methods do not give the same result when comparing concentrates and plasma. On average, two‐stage assays detect 20% more VIII:C activity in concentrates as compared to plasmas than do one‐stage assays.