LDL cholesterol

LDL is the transport particle (lipoprotein) that brings cholesterol from the liver to the body's cells; in the vessel wall it can be retained and oxidised. Oxidised LDL (ox-LDL) triggers plaque formation. Oxidised LDL can be looked at as an additional value.

What LDL does in the body

LDL forms in the blood from VLDL released by the liver: lipoprotein lipase gradually removes triglycerides from VLDL, and via IDL a smaller, cholesterol-rich particle remains – LDL. Each LDL particle carries exactly one apolipoprotein B-100, to which the LDL receptor binds. The cell takes up the particle by invagination and uses the cholesterol for membranes or, in the adrenal glands and gonads, for hormones. The liver retrieves most of the LDL. How many receptors it forms depends on its own cholesterol content via the switch SREBP-2; the protein PCSK9 ensures that receptors are broken down instead of reused.

Low LDL – what happens in the body?

A low LDL value shows that the liver is taking up LDL promptly via its receptors or releasing little VLDL. The body's cells then cover more of their cholesterol needs through their own production. Low values occur with an overactive thyroid, malnutrition, severe liver disease, disorders of fat absorption, acute inflammation and with cholesterol-lowering medications, as well as with inherited variants, for example when PCSK9 is less active. In rare inherited disorders of apoB production, the fat-soluble vitamins can additionally be transported less well, and fat accumulates in the liver because it cannot export enough of it as VLDL.

High LDL – what happens in the body?

When LDL rises, the particles stay longer in the blood – usually because fewer or less effective LDL receptors are taking them up. This occurs with inherited variants in the LDL receptor, apolipoprotein B or PCSK9 (familial hypercholesterolaemia), with an underactive thyroid, after the menopause, and with kidney disease and bile congestion. The more LDL particles circulate, the more penetrate the inner vessel wall. There they are retained by connective tissue fibres and oxidised; scavenger cells take up oxidised LDL unchecked via scavenger receptors and become foam cells, from which plaques develop. At very high values, cholesterol is also deposited in tendons and eyelids.

The interpretation is given in your report.