To examine the impact of a new international reference preparation for serum proteins on the among-manufacturer variance in the College of American Pathologists Surveys.
The results of the Surveys for the years 1993-1998, supplied by the College of American Pathologists.
Mean values for manufacturers' assays were compared for each protein in the quality control samples. Results were separated by the reported reference material from which values for calibrators had been transferred. Standard statistical parameters (means, standard deviations, and coefficients of variation) were calculated from the reported means.
Among-manufacturer coefficients of variation have dropped significantly for most serum proteins since the introduction of the new reference material. Possible reasons for continued differences are discussed.