Background :In order to evaluate the bias of quality control materials used in the clinical chemistry testing, and to examine the behavior of different types of control materials, the author developed the following experimental design. Method :Five sets of lyophilized control materials including normal and abnormal levels from five different manufacturers and one pooled serum prepared in our laboratory were analyzed by Hitachi 747 automated chemistry analyzer and Nucleus automated electrolyte analyzer for the determination of total protein, albumin, totalbilirubin, direct bilirubin, total cholesterol, alkaline phosphatase, aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, glucose, uric acid, blood urea nitrogen, creatinine, `Y-glutamyl transferase, calcium, phosphorus, creatine kinase, sodium, potassium, chloride, amylase and triglyceride. Result :The CVs of imprecision study for the instruments using control materials were below 0.9%, 1.9%, and 3.6% respectively in the within-batch, inter-batch and between day precision analysis. The evaluation of the bias of the 11 control materials according to the storing conditions, including room temperature, refrigeration at 6`C and freezing at -2OC, revealed that TP, ALB, T-Chol, BUN, Na, K, Cl, amylase and TG were most stable, and their CVovr(CVover all) was less than 5%. It was also reconfirmed that total and direct bilirubin were unstable in room temperature with light exposure and revealed 7%-34.5% of CVovr. ALP in room temperature was also unstable, but other enzymes were stable with 5%-10% of CVovr. The CVs of AST and ALT were especially high up to 24.5% and 27.2% respectively in El. The CVs of CK were up to 51.4% in E2. The CVs of frozen pooled serum as an economic control material was usually below 5.0%, except for 14.2% in AST and 5.1% in ALT. Conclusion :In summary, the behavior and bias of 5 different sets of lyophilized control materials seemed to be not significantly different each other, and it also suggests that frozen serum pools prepared in our own laboratory can be in use for control of internal quality assurance with low cost.

Keywords: Quality control, Control material, Bias