Between and within calibration variation: implications for internal quality control rules.

The variability between calibrations can be larger than the within calibration variation for some measurement procedures, that is a large CV:CV ratio. In this study, we examined the false rejection rate and probability of bias detection of quality control (QC) rules at varying calibration CV:CV ratios. Historical QC data for six representative routine clinical chemistry serum measurement procedures (calcium, creatinine, aspartate aminotransferase, thyrotrophin, prostate specific antigen and gentamicin) were extracted to derive the CV:CV ratios using analysis of variance.