The evolution and limitations of accuracy and precision standards.

Limits of maximum allowable analytical imprecision have been defined on the basis of normal range (Tonks), composite biological variation (Cotlove), intraindividual biological variation (Aspen Conference, College of American Pathologists), medical significance (Barnett, Skendzel), and a combination of medical significance and biological variation (Fritsche. Klee). Because error limits based on medical significance are less stringent than those based on biological variation, performance goals based on medical significance are more likely to be attained by laboratories than those defined by biological variation. Most clinical scientists realize that the goal to limit the analytical C.V. to one-half or less of the biological C.V. is arbitrary, and for the large majority of laboratory tests of no benefit to the patient, for the major component of total variation is not the analytical imprecision, but the intraindividual variation itself. Furthermore, the purpose of laboratory testing is to help physicians confirm or exclude potential diagnoses and monitoring therapy rather than detecting small deviations from normal values. Small changes in test values are quite often uninterpretable or lead to costly albeit fruitless investigations. In view of diminishing resources for health care we must establish the accuracy and precision required for each test. While improving the accuracy of some tests would be desirable, for most of them further improvement would be irrelevant to patient care because few tests are pathognomonic by themselves and quite often diagnosis is not made on the basis of a single laboratory result. If more accuracy is desirable, it must also be affordable and benefits should outweigh costs.