Detecting failed WBC-reduction processes: a quality assurance program introduced in a blood center

BACKGROUND: Pragmatic yet statistically valid quality assurance (QA) progra ms are necessary so that blood centers can select, validate, and monitor th eir WBC-reduction processes. A QA system for WBC-reduction processes based on the practical application of statistical theory within a large blood cen ter was developed. The system identifies parameters for procedure and compo nent evaluation and provides sample size and formatting suggestions. STUDY DESIGN AND METHODS: Analyses of both procedure and component performa nce were undertaken during the purchase, validation, and control of filtrat ion and apheresis WBC-reduction processes at Blood Centers of the Pacific f rom 1997 through 1999. QA analysis was categorized on the basis of whether the process was new to the organization or was a modification of a previous ly validated system. The numbers of samples necessary to consistently detec t failure in platelet yield, unit volume, pH, and WBC count was statistical ly determined by parametric and nonparametric techniques. RESULTS: Parametric analysis (power analysis) of the mean +/- SD of smaller numbers of samples was highly sensitive to shifted distributions, but only if the shift was normally distributed. Nonparametric analysis, necessary w hen the nature of the underlying distribution is unknown, suggested a minim al sample of 40 was required to achieve high confidence that significant bi modal failure (a secondary population with WBCs 5% above the cutoff) would be detected. CONCLUSION: A QA system, developed for the evaluation of new or revised WBC -reduction processes, was based on statistical analysis of normally and non -normally distributed process failure. The number of samples was determined that allowed the achievement of confidence and tolerance levels considered appropriate within the blood center. Suggestions for outlier evaluation an d a format for performance documentation have also been developed. To bette r define blood center quality goals, fur ther research is necessary on dono r and component biologic variability and the most significant modes of WBC- reduction process failure.