Enzymatic determination of lipids in human bile without bilirubin interference: reliable assessment of the cholesterol saturation index (CSI).

We describe a simple and rapid, but nevertheless precise and accurate method for the enzymatic determination of the main lipid constituents in human bile. Interfering bile pigments, especially bilirubin are eliminated by the use of aminopropyl bonded phase columns ("Bond-Elut") prior to the enzymatic measurement of cholesterol and lecithin. Intra-assay imprecision was between 3.1 and 4.9% CV, while the inter-assay figures were rather higher at 4.6 to 7.5% CV. Recoveries of bile salts, lecithin and cholesterol were between 94 and 103%. In contrast, the direct enzymatic determination in native bile produces falsely low results: lecithin from 5 to 20%, cholesterol from 25 to 40% of the true value. The results of both enzymatic methods correlated well with commonly accepted procedures for phospholipid and cholesterol determination. When compared with methods of bile lipid analysis involving solvent extraction, the column separation followed by enzymatic determination has the advantage of being simpler and less time consuming, without need of high-cost equipment, e.g. gas chromatography.