Multicenter study on purified protein C concentrates and defined plasma levels

: A variety of protein C assays are available as commercial kits. A collaborative study was undertaken to evaluate the performance of protein C assays. Various samples including calibrated plasmas and high purity concentrates destined to therapy were distributed among five laboratories. This comparison of protein C assays indicates that protein C levels measured by different functional or immunological assays and by five laboratories are very close for calibrated plasmas but not for high purity concentrates. The selection of the standard and the dilution buffer for protein C concentrates have important implications for the interpretation of the results. Dilution of purified protein C concentrates in protein C deficient plasma which restaure a total protein level similar to that of normal plasma improve the accuracy of functional protein C assays.