Hypercholesterolemia is the presence of high levels of cholesterol in the blood. It is a form of “hyperlipidemia” (elevated levels of lipids in the blood) and “hyperlipoproteinemia” (elevated levels of lipoproteins in the blood). Cholesterol is a sterol, a sort of fat; see the diagrammatic structure at the right. It is one of three major classes of lipids which all animal cells utilize to construct their membranes and is thus manufactured by all animal cells.