Proficiency testing of factor VIII:C activity assays at the Canadian Red Cross Society National Reference Laboratory.

A national proficiency testing program has been established to monitor the accuracy and precision of factor VIII:C (FVIII:C) assays performed at the various Blood Services Centres of the Canadian Red Cross Society involved in the collection and processing of either donor blood designated for component production or plasma destined for fractionation. This paper describes the preparation, design, and results of the first four exercises involving 19 laboratories. The exercises were designed to allow the investigation of intralaboratory variability between replicate samples and precision of assays as well as the causes of interlaboratory variability. The implementation of this program has led to improved precision and interlaboratory agreement on FVIII:C assays. These improvements were achieved mainly as a result of a modification in the method for sample dilution, an increase in both replicate testing of the same sample and the number of sample dilutions, and a reduction in the number of reagent systems used by various centres.