Methods of Quality Control

Abstract

In this paper no attempt is made to review the many analytical and statistical techniques which have been suggested for the maintenance of repro­ ducibility and accuracy in a clinical chemistry laboratory. Instead a description is given of the techniques which have been introduced into this laboratory over the past 7 years, with examples of their usefulness. Since no single technique of quality control is adequate in itself, six methods are sug­ gested in this paper. More would be used if they demonstrated errors which were not shown by our present techniques providing they did not make impossible demands on labour and personnel. Experience has shown that quality control tech­ niques are failing if it becomes necessary to reject a batch of tests following analysis and calculations. Prevention, based upon experience with quality control techniques, is possible and, particularly with the AutoAnalyzer, the batch can be controlled during processing of the specimens. Retrospective information of analytical methods drifting out of control is often not interpretable on one day's results, because no statistical technique detects a significant change on one day. A computer is used in two of the techniques described but at least one of these is widely prac­ tised in laboratories without a computer. Quality control techniques are not computer dependent but are easier with one. In the future there may be quality control techniques which cannot be performed without a computer. Display of results The greatest problem in quality control is not performing the techniques but interpreting them, and this is very dependent on the method of display­ ing the results. In this laboratory, the technician records the results obtained from control sera on a pre-printed form (Fig. 1) which is sent to the bio­ chemist responsible for quality control, who records the results and draws the appropriate graphs. Each section of the laboratory has a bench log book in which dates of changes in solutions, apparatus and techniques are recorded.