Errors in the Determination of Serum Cholesterol

SUMMARY Within the limits of the present study, the accuracy of determinations of cholesterol in human sera depends more on the purification of the cholesterol than on the colorimetric reaction used. The application of a variety of colorimetric reactions to an extract of non‐saponifiable material from serum gives values as accurate as the more complicated digitonide procedures. The accuracy of the principal methods for serum cholesterol determination are discussed in detail. In methods for preparation of the non‐saponifiable extract based on that of Abell, Levy, Brodie and Kendall (1952) simplicity of operation may be combined with accuracy. It is suggested the following points be established during standardization of methods omitting saponification. Since determination of cholesteryl stearate seems to be complicated by its insolubility in some colorimetric reagents for cholesterol, and in view of the colour developed with some of these reagents and polyunsaturated acids, identical molecular extinction coefficients should be obtained for cholesterol, cholesteryl stearate and the mixed cholesteryl esters of serum before the method can be judged accurate. The absence of effect of other serum constituents should then be verified by comparison of values obtained by the method and by application of the colorimetric reagent to the non‐saponifiable matter of serum. Internal standards should be prepared with methods using saponification. Cholesteryl acetate should not be used in the standardization of methods for serum cholesterol determination as its behaviour in many methods is not typical of the cholesteryl esters of serum.