Cholesterol is an essential component of cell membranes and required for the synthesis of hormones for development, growth and reproduction. It is also essential for the formation of bile acids that are needed to absorb nutrients from food. Cholesterol is obtained from dietary sources and is also produced by the liver.
However, excess cholesterol in the blood can be deposited on the walls of blood vessels leading to atherosclerosis and increased risk of heart disease and stroke.
Cholesterol and Lipoprotein Complexes
For transportation around the body cholesterol is incorporated into lipoprotein complexes – containing lipids and apolipoproteins. There are four classes of lipoprotein :
These are the smallest lipoproteins which transport triglycerides from the intestines to the liver, skeletal muscle and adipose tissue.
Very low density lipoprotein (VLDL)
VLDL transports triacylglycerol, which is synthesised in the liver, to adipose tissue.
Low density lipoprotein (LDL)
Low Density Lipoprotein (LDL) transports cholesterol from the liver around the body where it is deposited in tissues and organs
High density lipoprotein (HDL)
High Density Lipoprotein (HDL) is responsible for uptake and disposal of cholesterol.
HDL Cholesterol, or ‘Good Cholesterol’ is often measured in conjunction with LDL ("Bad Cholesterol") and Total Cholesterol as part of a lipid panel to screen for cardiovascular risk factors and monitor cholesterol reducing therapy. There is a strong negative relationship between the concentration of HDL cholesterol and coronary heart disease (CHD). Conversely a strong positive relationship has been reported between LDL cholesterol concentrations and the incidence of CHD.
Consequently each of these are used as a predictive test for patients at risk of developing CHD.
Other assays which may be of interest when measuring cholesterol are :
Non-Esterified Fatty Acids
Apo Lipoprotein A1
Apo Lipoprotein B