Fractionation of serum cholesterol: a critique.

A procedure for fractionation of serum cholesterol is developed by employing digitonin for the precipitation of free cholesterol in isopropanol. This method is based on the ferric acetate color reaction which is unaffected by traces of digitonin. It is influenced only negligibly by the presence of stanols in serum and is shown to be equally chromogenic with respect to both free and ester forms of cholesterol. The proposed procedure shows a three-fold improvement in precision (3.1 percent coefficient of variation [CV]) compared to that of the procedure by Leffler and McDougald (10.5 percent C.V.) which is based on the ferric chloride color reaction. The proposed free cholestrol procedure showed a mean recovery of 99.5% percent (98.1 to 102.5 percent) when cholesterol in 40 to 200 mg per dl concentrations was added to serum. The analytical performance of the proposed fractionation of serum cholesterol is critically reviewed with respect to its potential application in the diagnosis of liver diseases and in basic or experimental research.