Principles for developing improved quality control procedures.

Achieving quality goals in the clinical chemistry laboratory requires a comprehensive understanding of the many critical components and factors that are involved in a quality assurance program. The present paper has therefore been divided into sections dealing with quality goals as a rational starting point, determinants of quality for an analytical procedure, assessing the quality of a measurement procedure, assessing the quality of an internal control procedure, improving the quality of internal control procedures, designing an internal control procedure to provide a specified level of quality, strategy for implementing high power control procedures, implications of frequency of errors and predictive value theory on design of control procedures, role of external quality assessment in achieving quality goals, tools needed to improve quality control, and further considerations in achieving quality goals. In designing control procedures we have focused mainly on internal statistical control, emphasizing the new aspects of frequency of analytical disturbances. Less detailed consideration has been given to external quality assessment, though this problem area is also essential to a quality assurance program. Many other aspects have not been discussed, e.g., requirements for control materials, and use of patient specimens for control purposes, though both aspects are obviously very important. Even with these limitations, we think that quality control can be improved by development of better control procedures following the principles outlined here.