Process control procedures to augment quality control of leukocyte-reducedred cell blood products

Quality control of leukocyte-reduced packed red cell units (LRprc) produced in blood facilities must conform to regulatory criteria, which state that units may not contain more than 1 X 10(6) to 5 X 10(6) white blood cells (W BC) per unit. The post-filtration WBC content of a total of n = 386 LRprc u nits was counted with a Nageotte chamber to model the probability that a un it would not meet the regulatory criteria. The distribution of the residual leukocyte counts is close to a negative binomial distribution (NBD) and is independent of the packed red cell volume filtered. The observed probabili ty that a unit of blood has a residual WBC greater than 5 X 10(6) is 2.6 +/ - 2.6 X 10(-3). A power analysis of the two-sample Kolmogorov-Smirnov (KS) test in this application shows that a sample size of 20 is sufficient for d etermining that the process is in control when an out of control process ha s a k NBD parameter greater than or equal to that of the in control process . The three out of control processes observed to date appear to have this p roperty. A sample of size 80 may be necessary for confirming that process v alidation data sets conform to the larger 'reference' database (n = 386) fo r processes that are out of control in such a way that their k NBD paramete r is less than the k parameter of the in control process. Copyright (C) 199 9 John Wiley & Sons, Ltd.