RESUMEN
Two batches of lyophilized control serum, LYOPHIL (M.Tech. Diagnostics, Thailand) and VALIDATE (General Diagnostics, USA) were distributed weekly as blind internal quality control for our central clinical chemistry laboratory. The precision of 19 biochemical tests was studied. We found that the routine condition variance (RCV) of most tests was not greater than the RCV claimed by Wilding at al except for the test of chloride and amylase. Chisquare test and Youden plot were used to analyze the two batches of control serum. The results show good correlation for both in and out control except for creatinine and phosphate. Consistency of the biochemical tests in both batches was evaluated by analysis of variance (ANOVA) of sets of consecutive 10-week period means for 1 year. Most of the mean values of each test in LYOPHIL and VALIDATE were not significantly different except those of bilirubin and creatinine (p>0.05).