Use of the Du Pont aca to measure cholesterol in high-density lipoprotein fractions prepared by the heparin/Mn2+ precipitation method.

The enzymatic cholesterol method used with the Du Pont aca has been modified to provide a reliable measurement of high-density lipoprotein cholesterol in serum after heparin/Mn2+ precipitation of the low- and very-low-density lipoproteins. Interference by Mn2+, equivalent to about 90 mg of cholesterol per liter, is decreased to less than 40 mg of cholesterol per liter by the presence of ethylenediaminetetraacetate (8 mmol/liter) in the diluent; the residual effect of Mn2+ is compensated by calibrating the aca with standards containing Mn2+ and heparin. With an 80-microliter sample, the sensitivity is 236 muA/mg per liter and linearity ranges from 50 to 1500 mg/liter. Average analytical recovery of cholesterol added to the high-density lipoprotein fraction was 103%. Diluted fractions give the expected results. Between-run reproducibility (CV) is 1.3 and 1.6% at 463 and 554 mg/liter. Correlation with the Lipid Research Clinics' procedure (25 samples) gave a regression line of y(aca) = 1.039x- 15, and a correlation coefficient of 0.997.