The Usefulness of Internal Quality Control Procedure Using External Quality Control Materials

Kim, Yun Hee

Abstract

BACKGROUND: It is very important to keep the quality of the process of clinical tests and for that internal & extenal quality control procedures are performed in many clinical laboratorys. With the simultaneous use of external quality control materials for internal and external quality control procedures, not only precision but also bias presumed to be systematic error can be assessed. Also the control limits for internal quality control procedure can be obtained. It is the aim of this study to investigate the useful aspects of the integration of internal and extenal quality control procedures.
METHODS
The Korean Association of Quality Assurance for Clinical Laboratory 2006-CC-01 quality control materials for external quality control survey were tested on 19 general chemistry items with Hitachi 7180 (Hitachi, Tokyo, Japan) autoanlyzer once a day for 20 days. Current means and standard deviations(sd) were obtained from internal quality control results for 20 days and were used to calculate the biases with target means from external quality control survey results. Bias, sigma(TEa/sd), method sigma(TEa-|bias|/sd) and total error(TE) of each the 19 items were calculated and the calculated total errors of 19 items were compared with the CLIA'88 allowable total errors(TEa). Contol limits for internal quality control procedures were established according to the method sigma levels and probability for false rejection(Pfr), probability for error detection(Ped), average run length for false rejection(ARLfr) and average run length for error detection(ARLed) according to the control limit levels were estimated.
RESULTS
Out of total 19 items, 8 items such as albumin, glucose, triglyceride, total cholesterol, uric acid, total bilirubin, GGT and LDH satisfied the CLIA'88 TEa criteria and 11 items such as total protein, total calcium, inorganic phosphorus, BUN, creatinine, AST, ALT, ALP, sodium, potassium and chloride didn't satisfied. In the 11 items not satisfying CLIA'88 TEa criteria, 6 items such as BUN, creatinine, AST, ALT, sodium and chloride had the method sigma below 1.65 and control limits for internal quality control procedure could not be established. Control limits of the other 13 items were established according to the method sigma leves. In case of 6 method sigma level, Pfr were estimated to be 0.000007 and Ped to be 1.0000 and ARLfr to be 146910 and ARLed to be 1.00.
CONCLUSION
The integrated data from both the internal and external quality control results were very useful in assessment of the quality status of the tests and in designing and planning the internal quality control procedures such as control limits.