Non-HDL Cholesterol Test
Aged 40 as part of a routine cardiovascular health check, or if you are already thought to be at risk of cardiovascular disease for another reason, or if you are taking (or are about to start) treatments which lower cholesterol.
Testing for non-HDL cholesterol requires a blood sample. Most often, the blood sample is collected by venepuncture (using a needle to collect blood from a vein in the arm). Occasionally a finger prick test can be used, although this is not commonly available in GP practices or hospitals in the UK.
Measuring non-HDL cholesterol does not require fasting. However, you should follow your health care professional's advice, as fasting might be needed for other tests being performed.
Cholesterol is carried in the blood on protein particles called "lipoproteins". A number of different types of lipoproteins exist, but they can be divided into high density lipoproteins (HDL), and everything else (non-HDL). The distinction is made on the basis of the different functions of HDL vs non-HDL. All non-HDL particles carry their cholesterol from the liver and deposit it in the walls of arteries, whereas cholesterol on HDL is carried in the opposite direction. The implication of this is that non-HDL cholesterol (non-HDL-C) is "bad", as it causes "furring up of the arteries" (atherosclerosis), which can lead to cardiovascular disease such as heart attacks and strokes. On the other hand, HDL cholesterol is known as good, as low concentrations are associated with atherosclerosis.
One of the main components of non-HDL-C is LDL-C. Previously, LDL-C was used as the main measure of "bad" cholesterol. However, it is know recognised that other forms of non-HDL are also harmful, and not just LDL. Therefore, non-HDL-C is preferred to LDL-C in risk assessment. As well as LDL, non-HDL lipoproteins include very low density lipoprotein (VLDL), intermediate density lipoprotein (IDL), lipoprotein remnants, and lipoprotein (a).
Non-HDL-C, is not directly measured by the laboratory, but is a calculated value determined from direct measurements of both total cholesterol and HDL-C. The various components of non-HDL-C, listed above, are not usually measured.
How is it used?
Your doctor will look at your non-HDL cholesterol as part of a lipid profile during cardiovascular risk assessment, as it is one factor which influences your risk of developing cardiovascular disease in the future. If your non-HDL is high, it puts you at higher risk, as non-HDL particles deposit their cholesterol in the artery walls, predisposing to blockages.
An important reason to measure non-HDL is if you are taking, or are about to start taking cholesterol-lowering treatments such as statins. Changes in non-HDL after starting treatment give an indication on how well the treatment is working.
When is it requested?
Non-HDL is measured as part of a lipid profile, which is commonly checked by your GP after you reach the age of 40 for a routine cardiovascular health assessment. The lipid profile, including non-HDL, may be checked at other times if you are thought to be at increased risk of cardiovascular disease for another reason.
As indicated above, when treatment or lifestyle changes are being considered to help lower cholesterol, non-HDL should be measured as a "baseline". It will then be re-measured once the treatment or lifestyle change has started, to determine how well you have responded, and if any further interventions are required.
What does the test result mean?
There is no set "normal" or "abnormal" value for non-HDL cholesterol. However, high values are associated with increased risk of cardiovascular disease, so the lower it is, the better.
When treatment is started to lower cholesterol, changes in non-HDL cholesterol are the main indicator of how well the treatment is working. The current recommended target is a 40% reduction from the pre-treatment value, to indicate a good response (which is the predicted response to standard doses of statins).
Is there anything else I should know?
Cholesterol, including non-HDL cholesterol, should ideally be measured when a person is healthy. It is temporarily low during acute illness, immediately following a heart attack, or during stress (like from surgery or an accident). To get a true representation of your cholesterol, you should wait at least six weeks after any illness before having it measured.
In women, cholesterol is high during pregnancy (and after the menopause). Women should wait at least six weeks after the baby is born to have cholesterol measured.
Some drugs that are known to increase cholesterol levels include oral corticosteroids, beta blockers, oral contraceptives, thiazide diuretics, oral retinoids and phenytoin.
What is the difference between non-HDL cholesterol and LDL cholesterol?
For many years, LDL cholesterol has been used as the main indicator of "bad" cholesterol, i.e. the kind which tends to get deposited in arteries and leading to heart attacks and strokes. However, evidence has accumulated that cholesterol carried on lipoproteins in addition to LDL can also be harmful. So, non-HDL includes LDL and all the other harmful lipoproteins and is therefore thought to be a better indicator of future cardiovascular risk than just LDL. In fact, the amount of cholesterol carried on VLDL (one of the kinds of non-HDL) is increased in obesity, and as more and more people become overweight, using non-HDL is particularly important.
The other benefit of using non-HDL rather than LDL cholesterol is that non-HDL doesn't require fasting before the sample is taken, whereas LDL does.