Rapid semi-micro procedure for estimating free and total cholesterol.

THE NEED for a simplified, rapid, and reliable procedure for estimating accurately total cholesterol and cholesterol esters in the clinical laboratory is apparently fulifiled by the FeCl3-H2S04 method. The procedure under discussion is essentially a modification of the methods developed by Zlatkis et at. (1) and Zak et at. (2); it has satisfactorily passed rigid evaluations in serum survey participations and with the use of reconstituted lyophilized control serum during a period of over one year. The success of this colorimetric procedure is presumably attributable to the critical ratio of glacial acetic acid and concentrated sulfuric acid containing phosphoric-acid--dissolved fernc chloride. The results obtained with this procedure compare favorably with those obtained with the saponification methods of Schoenheimer and Sperry (3) and Abell et at. (4), and are remarkably reproducible (Tables 1 and 2). Interference of bromide and iodide in the color reaction is easily eliminated (5). A stable iron reagent is employed (6). The stability of the purple color produced (Kiiani reaction) is such that the color will not fade appreciably when exposed to sunlight for several hours. Accurate determinations can be attained with the simplest photoelectric colorimeters as well as with spectrophotometers at wavelength 550 m/L (green filter) (Table 3).