IN-VIVO RECOVERY WITH PRODUCTS OF VERY HIGH-PURITY - ASSAY DISCREPANCIES

In view of reports of FVIII assay discrepancies in post-infusion plasm a samples depending on methods used, we compared FVIII results run by each of four different methods following infusion of rFVIII (Kogenate( R)). Nine persons with haemophilia A were infused with each of two lot s of product. Plasma samples were obtained at baseline, and at 10 min, 30 min, 1, 2, 4, 8, 12, 14, 30 and 48 h post-infusion for measurement of FVIII. FVIII assay methods were chromogenic, and one-stage APTT us ing three different types of activators: micronized, silica, ellagic a cid, and kaolin. The same reference plasma standard was used throughou t. Results demonstrated a consistent difference in FVIII values, with chromogenic assays being considerably higher than those run by one-sta ge assays. The discrepancy was greatest when kaolin was the activator. These results point out the problems in attempting to determine the ' 'correct'' FVIII level in patient plasma samples following infusion of high purity FVIII preparations. Potential ''pitfalls'' include the st andard used for defining product potency, the methods, reagents, instr umentation and standards used in assaying plasma samples and, in some instances, the characteristics of the product itself. This situation h as considerable cost implications, potential impact on patient care, a nd makes it difficult to compare results between laboratories.