Comparison of Pooled Fresh Frozen Serum to Proficiency Testing Material in College of American Pathologists Surveys: Cortisol and Immunoglobulin E

Abstract Context.—The College of American Pathologists (CAP) provides proficiency testing (PT) surveys to laboratories around the world. Objectives.—To compare diagnostic assay methods for serum/plasma cortisol and immunoglobulin (Ig) E in terms of their bias and precision, to determine how well CAP PT specimens simulate human serum, and to reassess proficiency test grading criteria in light of these findings. Design.—A participant-blinded, prospective trial. One vial of pooled fresh frozen serum (FFS) and 4 different admixtures of PT material (PTM) were sent to laboratories participating in PT surveys. Participants.—Laboratories providing cortisol (>1000) or IgE (>230) results among the subscribers to the CAP surveys, Ligand (General) 2003, set K/KN-A and Chemistry 2003, set C-C. Main Outcome Measures.—The main outcome measures were (1) bias among laboratories using the same method (peer groups), defined relative to the median of method means (MedMM); (2) imprecision as measured by the SD and coefficient...