Comparison of laboratory performance with blind and mail-distributed proficiency testing samples.

PROFICIENCY TESTING (PT), in which samples are distributed by mail, has served as a basis for evaluating the competence of clinical laboratories for some time. The proponents of such testing have recognized its value as well as its limitations (1-5) . In recent years the Center for Disease Control (CDC), in administering the Clinical Laboratories Improvement Act of 1967, has received some disturbing reports of serious misuse of this testing system (6, 7). Some laboratories reportedly have regularly sent their proficiency test samples to more competent laboratories for evaluation, so that the results have not reflected the work of the laboratory being tested. Directors of competent laboratories and others knowledgeable in the field lhave expressed the opinion that in many instances mailed proficiency test samples only provide a measure of the most competent employee in the laboratory rather than of the employee who routinely tests patients' specimens. These commentators contend that the performance of laboratories is thereby made to appear better than it actually is, so that physicians are falsely reassured of the accuracy of laboratory work. The studies reported in this paper were designed to determine whether laboratories serving drug treatment centers and associated hospitals performed better with recognized proficiency test samples than with identical samples that were not recognizable as being test samples. One study was conducted in 1973 and another in 1975.