A new concept for quality control of clinical laboratory investigations in the light of clinical requirements and based on reference method values.

Quality control is an essential element in clinical laboratory investigations. In the basic programs for quality control used in recent years accuracy control has been carried out through a comparison with method-dependent assigned values. With this system the "accuracy" of results from different laboratories is relative, and comparability is assured only when the laboratories use the same analytical method. Considering the steadily increasing variety of methods and equipment, a meaningful exchange of information in patient care, teaching and research is becoming more and more difficult; but clinical requirements make such an exchange essential. In this paper a new concept for quality control is presented for discussion. In the basic program incorporating the new concept the method-dependent assigned values are replaced by reference method values, which are method-independent. In addition to accuracy control, an ongoing monitoring procedure using a Shewhart control chart is also carried out. The maximum allowable day-to-day imprecision and the maximum allowable deviation from the reference method value are fixed on the basis of clinical requirements. This means that the ratio of biological variation to analytical between-day imprecision should be greater than or equal to 2. If the biological variation is unknown, then the reference interval is used in its place; the quotient, reference interval/analytical between-day imprecision, should then be greater than or equal to 8. The decision limits for the interlaboratory surveys should be fixed in an analogous manner independent of the analytical method. After the introduction of quality control based on the new concept the results from different laboratories would be comparable to the extent dictated by clinical requirements. The main principles underlying the new concept and the effects of using the new approach are presented for discussion, and the reader is invited to submit comments in writing.