LDL cholesterol

Most UK laboratories print an upper limit of 3.0 mmol/L for the general population. LDL is usually calculated from the other lipid values rather than measured directly, and many labs leave it blank when triglycerides are above 4.5 mmol/L because the calculation is unreliable.

LDL stands for low-density lipoprotein, the particle that carries most of the cholesterol in the blood out to the tissues. It is the fraction most closely linked to the build-up of fatty deposits in artery walls, which is why it is often called the 'bad' cholesterol. In most UK laboratories the figure is calculated from total cholesterol, HDL and triglycerides rather than measured on its own.

Doctors use it as part of the lipid profile when looking at heart and circulation health, and to follow the effect of diet changes and cholesterol-lowering medicines over time.

• A diet high in saturated fat
• Family patterns of high cholesterol, such as familial hypercholesterolaemia
• An underactive thyroid
• Kidney disease with protein loss in the urine, and some liver conditions
• Some medicines, including steroids

• Cholesterol-lowering medicines such as statins and ezetimibe
• Weight loss and a diet lower in saturated fat
• An overactive thyroid
• Long-term illness and poor nutrition
• The weeks after a heart attack, surgery or serious infection

• It is usually calculated, so a high triglyceride level on the day makes the figure less accurate
• It falls for several weeks after any acute illness
• Different laboratory methods and calculations give slightly different figures

No fasting needed for the routine test, although a large fatty meal shortly before can make the calculated figure less accurate. Read alongside total cholesterol, HDL and non-HDL cholesterol.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.