A Novel Test for the Measurement of Skin Cholesterol

Increased serum cholesterol is a risk factor for atherosclerosis and coronary artery disease (CAD) (1)(2). Reduction of serum cholesterol has, therefore, been targeted for the prevention and management of CAD with cholesterol screening and is the primary tool for initial risk assessment (3)(4). Cholesterol, however, can also be quantified in skin.Skin reflects the vascular changes associated with age and aortic atherosclerosis. A simple, noninvasive procedure for the estimation of skin cholesterol, the “three-drop” test, has been proposed as an alternative screening method (5). The test, which uses three different concentrations of a digitonin–copolymer–horseradish peroxidase (HRP) conjugate and visual scoring, is capable of discriminating among healthy individuals, those at risk of developing atherosclerosis, and those with overt disease. Cholesterol 1,2,3TM is a refinement of this procedure. We describe here some properties of this test and report on our initial evaluation in a prospective clinical trial.Cholesterol 1,2,3 uses quantitative interpretation and a single concentration of detector. Briefly, the detector and the positive control each are added to die-cut wells in a foam template affixed to the palm. After a 1-min incubation, the reagents are removed by blotting and the HRP substrate is added to these wells and to a third well, which serves as negative control. After an additional 2-min incubation, color development in the center test well is measured by reflectance with a hand-held instrument (MD22 Spectrophotometer; X-Rite, Inc.) interfaced with a computer, and the result is reported numerically as the hue. Assay validity is assessed by visual interpretation of control wells.The specificities of digitonin conjugates have been demonstrated previously with several model systems [crystalline cholesterol, cholesterol-rich tissue sections, and antibody-immobilized LDL-cholesterol (LDL-C)], and the amount of skin-bound conjugate has been shown to correlate with epidermal cholesterol content (5). We extended the specificity …