Determination of Total and Esterified Choesterol in Serum

A simple method for the determination of total and esterified cholesterol is de-scribed. Serum lipids are extracted into a solvent mixture and aliquots of the extract are analyzed directly for free and total cholesterol by the Zlatkis reaction. Esterified cholesterol is calculated by difference. Free cholesterol is determined under con-ditions of temperature and solvent composition such that the cholesterol esters do not react. The method yields quantitative recoveries of free and esterified choles-terol from serum. Data are presented on the precision of the method, and on results of a comparison with the reference procedure of Sperry and Webb. ‘IHE CLASSIC METHOI) of analysis of “free ” and “esterified ” cholesterol in serum is based on precipitation of free cholesterol with digitonin, and subsequent measurement of this fraction by the Liebermann-Burchard reaction. The difference between the free cholesterol and the total cholesterol obtained in a similar way after hydrolysis of the esters gives the value of esterified cholesterol. This principle is the basis of the well-known methods of Schoenheimer and Sperry (1) and Sperry and Webb (2). Although highly regarded as reference methods, these procedures are too time-consuming for use in the routine clinical laboratory. A simpler approach is used in some methods where, under specific conditions, free cholesterol is determined by colorimetry in a lipid extract without recourse to purification by digitonin precipitation. Pursuing this idea, Girard and Assous (3) applied the Zlatkis reaction (4) to lipid extracts at 200 to determine free cholesterol and at 55-6#{176} to determine total cholesterol. in our hands this method did not give satisfactory results, primarily for the following reasons: A turbidity is developed during the determi-nation of free cholesterol that interferes significantly with the fina