Quality control and its importance in good laboratory practice- Review

Health care delivery is no longer a simple process of examining the patient and giving him a prescription. Over the years there has been rapid expansion in the various branches of health care services. As part of this expansion process and explosion of scientific medical knowledge. Quality Control (QC) is carried out in the laboratory to find out and reduce the errors in the analytical phase of the testing system prior to the release of reports of the patients. High quality laboratory results involve commitment to all phases of testing system including pre-analytical, analytical and postanalytical phases. Pre-analytical phase includes those factors which affect the laboratory results prior to the handling of the sample in the clinical laboratory. Post-analytical factors are those which affect the results after the analytical phase is complete. Quality control involves implementation of both Internal Quality Control (IQC) and External Quality Control (EQC) which is known as Proficiency Testing (PT). Internal quality control is performed daily in the laboratory using controls whose values are known, where as external quality control includes the participation of the laboratory in an external quality assessment scheme which is used as a test of competency. The interpretation of quality control data is done with the help of both graphical and statistical tools. Quality control data is most commonly visualized with the help of Quality Control (QC) charts which include Levey-Jennings (LJ) Charts and Westgard Rules. Both are useful in detecting trends or shifts observed from the average target value. In this paper, quality control in a clinical laboratory has been discussed with respect to potential errors in the laboratory, statistical quality control (SQC) tools, the procedures used to maintain quality in laboratory, corrective and preventive action (CAPA) and clinical audit of the laboratory.