Determination of plasma cholesterol: comparison of gas-liquid chromatographic, colorimetric and enzymatic analyses.

The efficacy of methods for plasma cholesterol analyses based on gas-liquid chromatographic (GLC) or enzymatic cholesterol determinations was tested on commercially available standard serum, plasma obtained in a study of an age stratum of the population and on plasma from a number of patients from an out-patient department. These results were compared with colorimetric cholesterol determinations on chloroform/methanol extracts from plasma using the ferric chloride/sulphuric acid reagent. The GLC-based procedure gave values 12% lower than the colorimetric determinations. This discrepancy seemed to be explained, to a marked extent, by the fact that cholesterol metabolites interfere with the colorimetric determinations. The GLC-based method was apparently accurate since it has the advantage of specificity and is easy to standardize with the internal standard technique. Enzymatic total cholesterol analyses gave slightly (2%) lower values than the GLC-based analyses, apparently because of an incomplete hydrolysis of cholesterol esters. Enzymatic analyses of free cholesterol gave similar results to those of the GLC-based method.