Experience with quality control in clinical chemistry.

The introduction of statistical quality control of clinical chemical analyses has not only provided documentation of the reliability of analytical results and led to improvements in reliability, it has also led to marked improvements in the methods, reagents, calibration materials, control specimens and equipment used. Beyond this, the availability of reliable analytical results has enabled further development of the theoretical concepts underlying thought and action in clinical chemistry. The present paper provides an overview of developments in quality control in the Federal Republic of Germany since 1964. The uniform basic program for quality control with control specimens, as set forth in the Guidelines of the Medical Society of West Germany and required in all states of the country since 1971, is described and our experience with it discussed. Internal quality control consists of separate precision control and accuracy control procedures. External quality control in the form of short-term interlaboratory surveys with control specimens provides an objective check on accuracy. The assigned values for the required accuracy control specimens are determined under routine conditions in particularly well-equipped and well-staffed laboratories headed by particularly highly qualified individuals. The laboratories are independent of the manufacturers of control specimens, calibration materials, reagents and equipment. Over the years, the assigned value determinations have also provided valuable information about the structure of the data and about the reliability criteria for the analytical results. Based on the experience gained with this system, a new concept for quality control was developed in which the method-dependent assigned values are replaced by method-independent reference method values. The requirements for quality control, i.e., the maximum acceptable imprecision and the maximum acceptable deviation of the analytical results from the reference method value or the assigned value, are specified after consideration of the clinical requirements, that is, their effects on medical decision-making.