The concept of precision extended to the atherogenic index of plasma

Background The atherogenic index of plasma (AIP), defined as the base 10 logarithm of the ratio of plasma triglyceride (TG) to high density lipoprotein cholesterol (HDL-C), has been employed as a predictor of cardiovascular risk. We seek to quantify the analytical precision of the AIP using the coefficients of variation (CVs) of the TG and HDL-C assays. Methods Error propagation methods are employed to develop a simple formula for the standard deviation of the random analytical error in the AIP assuming that the errors in the TG and HDL-C assays are normally distributed. An alternative derivation assuming log-normal distribution of errors gives nearly identical results while avoiding subtle technical problems. Results The SD of the AIP is given by and this formula will provide SD results that are accurate within 0.4% for CVs of TG and HDL-C less than 5%, as compared with results of Monte Carlo simulation. We also explain that the concept of CV cannot be applied to the AIP since it is a logarithm. Conclusions The formula provides a simple means to quantify the precision of the AIP from precision data available for the TG or HDL-C assays.