Determining the adequate number of internal quality control levels: the example of coagulation factor VIII assay.

Taking the specific case of coagulation factor VIII assay, we determined the characteristics of an internal quality control panel assuring control of the assay method for all of the critical factor VIII concentrations. The precision of the assay method was determined on six control materials C1-C6, with expected factor VIII levels of 1, 5, 30, 50, 80 and 150 U/dl, respectively. Given that, when two control levels correlate statistically, the information provided by one of them is redundant, we used correlation and principal components analysis to define a priori adequate and inadequate control panels.