HDL cholesterol: why low matters and high is not a free pass

Cholesterol is carried in blood inside particles called lipoproteins, named by their density. HDL, or high-density lipoprotein, particles are often described as returning cholesterol toward the liver. The HDL cholesterol test measures the cholesterol they carry. Lab Tests Online UK explains that it is used to screen for the risk of developing cardiovascular disease and to monitor treatment.

Cholesterol itself is vital: it is part of cell membranes and the starting point for several hormones. The NHS says high cholesterol is when there is too much of this fatty substance in the blood, which can block blood vessels and raise the chance of heart problems or stroke, and that it does not usually cause symptoms, so a blood test is the only way to find out.

HDL is usually requested with total cholesterol or as part of a lipid profile including non-HDL cholesterol and triglycerides, during the cardiovascular risk assessment offered from age 40. The NHS Health Check is a free check-up for people aged 40 to 74 without certain pre-existing conditions, invited every 5 years, that includes a cholesterol test and produces a ten-year cardiovascular risk score.

Lab Tests Online UK says the value entered into risk calculators such as QRISK is actually the total cholesterol to HDL ratio, the balance between the two, and that knowing your future risk can guide lifestyle changes or the decision to start medical treatment.

No fasting is needed for an HDL test or full lipid profile, although in some circumstances fasting is still required and you should follow the instructions you are given. The NHS says some people are asked not to eat for up to 12 hours but most do not need to fast. Blood is usually taken from a vein in the arm; finger-prick tests are sometimes used at NHS Health Checks.

HDL should not be measured when you are suddenly unwell. Cholesterol is temporarily low during sudden illness, immediately after a heart attack and during stress such as surgery or accident; wait at least 6 weeks after any illness. HDL may change in pregnancy, so wait at least six weeks after the birth.

Low levels are worse than normal levels. Lab Tests Online UK says the lower the HDL cholesterol, the higher the risk of developing cardiovascular disease, because low HDL implies LDL particles are smaller and denser than normal, which makes them more atherogenic, meaning more likely to cause plaque in the arteries. Common associations include smoking, inactivity, excess weight, high triglycerides and type 2 diabetes.

Raising HDL by itself has not proved a reliable way to cut risk; the practical approach is to treat the whole risk picture, including LDL cholesterol, blood pressure, smoking and glucose.

Whether a high HDL is a problem is uncertain. Lab Tests Online UK says higher than normal HDL is unlikely to have protective effects in most people, that if it is due to problem drinking there are no health benefits, that some families with inherited high HDL have less cardiovascular disease and some more, and that HDL metabolism is incompletely understood. Once HDL is normal, further increases appear to bring no further benefit.

If your lipid results and risk score suggest higher risk, the NHS says a doctor or nurse will discuss lowering cholesterol through diet changes or medicine, and statins are the most common medicine for high cholesterol, taken once a day and usually for life. Healthy eating, more exercise, stopping smoking and reducing alcohol are first steps. Do not stop prescribed medicines without advice. Chest pain, breathlessness or sudden weakness on one side are emergencies; call 999.