Review of proficiency testing performance of laboratories accredited by the College of American Pathologists.

The Commission on Laboratory Accreditation of the College of American Pathologists (CAP), Skokie, III, monitors the proficiency testing of accredited laboratories by regular review of the Cumulative Survey Management Report. Analytes are targeted for review on the basis of repeated "unacceptable" results in the CAP Survey Program. Approximately 1% of proficiency testing results are repeatedly graded unfavorably. Directors of 271 Great Lakes Region laboratories reported the causes of and the corrective actions taken for 583 targeted results over a two-year period. Targetting of results in 31% was attributed to methodologic or instrumentation problems, 19% to technical performance factors, and 27% to clerical errors. Only 3% were ascribed to the Survey materials or to the criteria used for grading, and 20% of the problems remained unexplained after investigation. There was improvement in 496 (88%) of 583 targeted. During the study period, results from 96% of laboratories showed improved performance for all or a majority of the targeted analytes.