Use of computer modeling to predict the magnitude of intralaboratory error tolerated by proposed CDC interlaboratory proficiency testing performance criteria.

In December 1987, the Centers for Disease Control (CDC) proposed to the Health Care Financing Administration revised criteria for evaluating participating laboratories' performance in proficiency-testing programs. If these criteria are accepted, they will become the minimum standard for all regulatory proficiency-testing programs. To evaluate a laboratory's performance in a clinical chemistry proficiency-testing program, the CDC proposed a combination of the use of fixed limits, multiples of the interlaboratory group standard deviations, and absolute values. In addition, laboratories would be required to meet 70% of the most recent proficiency-testing challenges. Because the purpose of regulatory proficiency testing is to identify poorly performing laboratories, it is essential that regulators be aware of the relationship between the regulatory criteria and the actual magnitude of intralaboratory error they tolerate. Through computer simulation, we determined for 21 chemistry analytes the amount of intralaboratory error tolerated by the CDC-proposed criteria. We evaluated the effectiveness of the proposed criteria by comparing the levels of total intralaboratory error permitted by a proficiency-testing program by using the CDC criteria with actual currently achievable levels of performance and defined medical usefulness needs. The proposed CDC criteria were too lenient for six analytes, about correct for seven, and too stringent on two; no medical usefulness limits were available for six.