FACTORS AFFECTING THE PERFORMANCE OF FACTOR-VIII COAGULANT ACTIVITY ASSAYS - RESULTS OF PROFICIENCY SURVEYS OF THE COLLEGE-OF-AMERICAN-PATHOLOGISTS

To evaluate sources of interlaboratory variation in factor VIII coagulant assays and the effects of uniform calibration on it, data were analyzed from Survey Set H2-C, 1987, of the College of American Pathologists, Northfield, Ill, into which the College of American Pathologists Reference Preparation for Factor VIII was incorporated. Peer group performance and its improvement by uniform calibration were evaluated by comparing means, precisions, and numbers of acceptable survey scores. Results showed a poorer performance by less experienced laboratories and by those that used undesirable calibrators. Substantial improvement was seen with uniform calibration, especially among laboratories that had employed poorer calibrators. Although variance component analysis showed that the type of calibrator was the most important contributor to interlaboratory variation, it accounted for only 10% of total variability. Participant summaries and questionnaires that spanned several years revealed steady improvement in methodology but no striking changes in interlaboratory variation.