Cholesterol is a sterol molecule and is an important structural component of all animal cell membranes to maintain both membrane structural fluidity and integrity. Cholesterol also acts as a precursor for the biosynthesis of vitamin D, steroid hormones and bile acids. Cholesteryl ester is an ester of cholesterol and can be hydrolyzed by pancreatic enzymes and cholesterol esterase to produce cholesterol and free fatty acids.

The Total Cholesterol and Cholesteryl Ester Colorimetric/Fluorometric Assay Kit provides a sensitive, simple and convenient way for detection of free cholesterol, cholesteryl esters, or both in various biological fluids based on colorimetric and fluorometric method. Majority of the cholesterol in blood exists in the form of cholesteryl esters which can be hydrolyzed to free cholesterol and fatty acids by cholesterol esterase. Cholesterol is then oxidized by cholesterol oxidase to generate H₂O₂ which reacts with a sensitive cholesterol probe to yield color (λmax = 570 nm) and fluorescence (Ex/Em = 535/587 nm). The assay can detect free cholesterol in the absence of cholesterol esterase or total cholesterol (cholesterol and cholesteryl esters) in the presence of cholesterol esterase in the reaction. Cholesteryl ester is determined by subtracting the value of free cholesterol from the total cholesterol.