External quality assurance of antithrombin, protein C, and protein S assays: Results of the college of american pathologists proficiency testing program in thrombophilia

And PS Assays Used by Labs. Participating in the U. States Coll. of Amer. Pathologists Proficiency Test. Prog. in Thrombophilia and to Grade the Perf. of Labs.. Des..-Standardized Norm. Plasma with Assigned Analyte Values Was Sent in 2 Separate Challenges to Participating Labs.. Participants Measured AT, PC, and PS Levels Using Loc. Methods. Results.-When Compared with the Assigned Values for the Intl. Std., the Order of Assay Accuracy from Highest to Lowest Was at Activ., PC Antigen, at Antigen, Total PS Antigen, PC Activ., PS Activ., and Free PS Antigen (Range of Assay Bias, 2.6%-8.8%). the Order of Assay Prec. from Highest to Lowest Was PC Activ., at Activ., at Antigen, Total PS Antigen, PS Activ., Free PS Antigen, and PC Antigen (Range of Assay Coefficient of Variation, 6.1%-20.0%). Most Test. Events (87.8%) Could be Graded as Pass or Fail Using A Target Range of 3 Std. Deviations from the Method-specific Mean. the Pass Rate Was 98.2% for All AT, PC, and PS Test. Events Comb.. Conclusions.-Accuracy and Prec. Were Higher for at Assays and Lower for PC and PS Assays. It Was Feasible to Grade Individual Lab. Perf. Context.-Hereditary and acquired deficiencies of antithrombin (AT), protein C (PC), and protein S (PS) are risk factors for venous thromboembolism. Proper diagnosis requires high-quality assays for these proteins. Objective.-To determine the accuracy and interlaboratory precision of AT, PC.