Hypercholesterolemia (literally: high blood cholesterol) is the presence of high levels of cholesterol in the blood . It is not a disease but a metabolic derangement that can be secondary to many diseases and can contribute to many forms of disease, most notably cardiovascular disease. It is closely related to the terms "hyperlipidemia" (elevated levels of lipids) and "hyperlipoproteinemia" (elevated levels of lipoproteins).

Elevated cholesterol in the blood is due to abnormalities in the levels of lipoproteins, the particles that carry cholesterol in the bloodstream. This may be related to diet, genetic factors (such as LDL receptor mutations in familial hypercholesterolemia) and the presence of other diseases such as diabetes and an underactive thyroid. The type of hypercholesterolemia depends on which type of particle (such as low density lipoprotein) is present in excess.

High cholesterol levels are treated with diets low in cholesterol, medications, and rarely with other treatments including surgery (for particular severe subtypes). This is also increased emphasis on other risk factors for cardiovascular disease, such as high blood pressure.

Signs and symptoms

Elevated cholesterol does not lead to specific symptoms unless it has been longstanding. Some types of hypercholesterolemia lead to specific physical findings: xanthoma (deposition of cholesterol in patches on the skin or in tendons), xanthelasma palpabrum (yellowish patches around the eyelids) and arcus senilis (white discoloration of the peripheral cornea).

Longstanding elevated hypercholesterolemia leads to accelerated atherosclerosis; this can express itself in a number of cardiovascular diseases: coronary artery disease (angina pectoris, heart attacks), stroke and short stroke-like episodes and peripheral vascular disease.

Diagnosis

When measuring cholesterol, it is important to measure its subfractions before drawing a conclusion on the cause of the problem. The subfractions are LDL, HDL and VLDL. In the past, LDL and VLDL levels were rarely measured directly due to cost concerns. VLDL levels are reflected in the levels of triglycerides (generally about 45% of triglycerides is composed of VLDL). LDL was usually estimated as a calculated value from the other fractions (total cholesterol minus HDL and VLDL); this method is called the Friedewald calculation; specifically: LDL ~= Total Cholesterol - HDL - (0.2 x Triglycerides).

Less expensive (and less accurate) laboratory methods and the Friedewald calculation have long been utilized because of the complexity, labor and expense of the electrophoretic methods developed in the 1970s to identify the different lipoprotein particles which transport cholesterol in the blood. In 1980, the original methods, developed by research work in the mid-1970s cost about $5,000, in US 1980 dollars, per blood sample/person.