A water-soluble cholesterol derivative for use in augmenting serum control materials

Cholesterol determination has been hampered by the lack of suitable means to prepare lyophilized serum control materials with an appropriate range of values. We prepared a water-soluble cholesterol derivative by first esterifying cholesterol with adipic acid and then reacting the cholesterol hemiadipate with Polyethylene Glycol 600 to form polyethoxyethanyl-cholesteryl adipate. The compound reacts quantitatively in several commonly used methods, including enzymic, extraction, and direct-assay procedures. When the additive is directly mixed with human serum that has been depleted of beta- and pre-beta-lipoproteins, an optically clear solution results for which cholesterol values are stable. The clarity is retained upon lyophilization and reconstitution. Addition of this cholesterol compound to partially delipidized serum appeared to have no significant effect on results of assay of 18 other commonly measured serum constituents.