Quantification of serum apolipoprotein B by infrared spectroscopy

While the conventional approach to assessing both the risk of coronary artery disease and the adequacy of therapy is LDL cholesterol testing, there is compelling evidence to suggest that apolipoprotein B (apoB) is superior to LDL cholesterol for both of these purposes. However, the measurement of apoB requires techniques that can be expensive and difficult to standardize. The aim of this study was, therefore, to develop a new method, based on infrared (IR) spectroscopy, for the routine quantification of apoB in human serum. A total of 366 serum samples were obtained from patients with various disorders. Small volumes (2 microl) of serum specimens were dried to films, and duplicate IR absorption spectra measured. The reference apoB concentrations were determined separately using a standard method, and the proposed IR method was then calibrated using partial least squares (PLS) regression analysis to quantitatively correlate the IR spectra with the reference results. The apoB concentrations predicted from the IR spectra of serum were highly correlated and in excellent agreement with those determined by the reference method. The correlation coefficient (r) for apoB was 0.94, with the standard error between IR-predicted and reference values was 0.10 g/L. In combination with earlier work demonstrating the accurate determination of LDL-C, HDL-C, total cholesterol, and triglycerides from a single infrared spectroscopic measurement, the addition of accurate apoB determination from the same spectrum makes the method very attractive for laboratory use in the routine evaluation of coronary artery disease risk.