Optimization of production variables governing yield and stability of factor VIII in cryoprecipitate

Abstract

Cryoprecipitates are used as the raw material for the preparation of Factor VIII (FVIIIl) for replacement therapy for haemophiliacs. Routinely, cryoprecipitate only recovers 50% of the Factor VIII in the plasma. The purpose of this study, production of cryoprecipitate, was to investigate those variables which play a key role in determining the yield of Factor VIII present in cryoprecipitate. Cryoprecipitate production involves a wide range of variables which could effect the final outcome of the product. These vary from the donor blood group, time of donation, exercise levels of the donor, to a time delay prior to processing, temperature storage conditions, to the method utilised for plasma freezing and thawing. The objective was to explore which combination of variables in the procedure would lead to a process which would optimize the preparation of cryoprecipitate in a routine environment, to yield the highest levels of Factor VIII. Frequently in scientific investigations, particularly when a practical approach has to be adopted, questions arise in which the effects of a number of different variables in a process, require evaluation. Such questions can usually be most economically investigated, by arranging the analysis according to an ordered plan in which all the factors are viewed in a regular way. Provided the plan has been correctly chosen, it is possible to determine not only the effect of each individual variable, but also the way in which each effect depends on the other factor, by means of an interaction. This makes it possible to obtain a more complete picture of what is happening, than would have been obtained by varying each of the variables one at a time while keeping the others constant. Designs of this sort lend themselves well to statistical analysis, and provide their own estimates of experimental error. This type of statistical analysis called, 2K Fractional Factorial Experimental Design, forms the basis of this study in which 14 key variables in the production process of cryoprecipitate were defined as possible areas in which Factor VIII levels in the cryoprecipitate are effected. Key variables have been identified on an individual basis in previous studies (Burka et al., 1975), however this blended approach to optimise the key variables within the production environment, and define further combinations which could be incorporated into the production, has never been attempted. The statistical design used in the study was compiled by the Institute for Biostatistics of the Medical Research Council (MRC). Units of blood were collected and processed, from blood donors under the stipulated criteria, corresponding to the study design.