A cholesterol test measures the total amount of cholesterol in your blood. It is often performed as part of a screening test called a Lipid Panel which is most often used to assess your risk of developing heart disease or stroke. It measures levels of cholesterol, LDL or low-density lipoprotein cholesterol and HDL or high-density lipoprotein cholesterol. Triglycerides, another form of fat, is also measured.
A higher than normal LDL often called "bad" cholesterol level is one of the most important modifiable risk factors for diseases of the blood vessels and your risk of having a stroke or heart attack. These conditions are known together as cardiovascular disease (CVD).
Over the years, many clinical trials have demonstrated that lowering LDL cholesterol in people with higher levels reduces the risk of having a stroke or heart attack in people with and without CVD.
Your doctor will make a judgement about whether LDL cholesterol lowering treatment should be started depending on your overall CVD risk. This risk calculation includes other CVD risk factors such as high blood pressure, age, diabetes, and smoking. Your heart and stroke risk score can be calculated using the calculator at www.cvdcheck.org.au/calculator.
What is being tested?
Cholesterol is a substance found almost exclusively in animals. Body fluids including blood and all cells contain some cholesterol which is needed for good health. It forms the membranes for cells and important in production of hormones and bile acids. Cholesterol in blood is in complex particles called lipoproteins. There are different types of lipoproteins. HDL, good cholesterol, removes bad cholesterol from the body, whereas LDL, bad cholesterol, collects in the walls of blood vessels. The test for cholesterol measures all cholesterol (good and bad).
Only a small amount of cholesterol comes from your diet, most is made in your liver. If you have an inherited predisposition for high cholesterol levels or if you eat too much of the foods that are high in cholesterol (e.g. liver, kidney and prawns), saturated fats (e.g. red meat, fried foods, poultry and full-fat dairy products) and trans fats (e.g. deep fried foods and certain baked foods), then levels of cholesterol in your blood may increase and have a negative impact on your health. However cholesterol in food is less important than eating less saturated and trans fats, and more healthy fats (monounsaturated and polyunsaturated fats, omega-3 and omega-6).
The extra cholesterol in your blood may be deposited in plaques on the walls of blood vessels. Plaques can narrow or eventually block the opening of blood vessels, leading to hardening of the arteries (atherosclerosis) and increasing your risk of numerous health problems, including heart disease and stroke.
How is it used?
To screen for risk of developing cardiovascular disease (heart disease, stroke and related diseases) and to monitor treatment.
When is it requested?
Cholesterol testing is recommended when you have established heart disease (angina, heart attack), or if there is a family history of high cholesterol, or of heart disease at an early age; if you are less than 45 years of age and have risk factors which put you at an increased chance of developing heart disease, such as diabetes, high blood pressure, chronic renal failure or renal transplantation, Aboriginal or Torres Strait Islander, overweight or you are a smoker. In addition, cholesterol testing is performed if you are following a recommended diet or taking drugs to lower your cholesterol level, to monitor your response to treatment. Total cholesterol may be measured alone or in combination with other tests including HDL, LDL, and triglycerides - often called a lipid profile.
What does the result mean?
The cholesterol level measured in your blood will be considered along with other risk factors for heart disease (high blood pressure, smoking etc.) when assessing your overall risk of developing heart disease. This overall assessment is what will be used to decide whether or not you require further treatment in the form of lifestyle changes such as diet, exercise or drugs to lower your cholesterol level.
A total cholesterol level of greater than 7.5 mmol/L is considered high risk. And also this level should be reviewed for family history and clinical features of familial hypercholesterolaemia which is an inherited condition.
If you are taking medication to lower your cholesterol, the target is to get your total cholesterol to a value less than 4.0 mmol/L.
Is there anything else I should know?
Cholesterol testing is recommended as a screening test to be done for all adults with no risk factors for heart disease at least once every four to six years. It is frequently done in conjunction with a routine physical examination.
Blood cholesterol is temporarily low during acute illness, immediately following a heart attack, or during stress (like surgery or accident). You should wait at least 6 weeks after any illness to have cholesterol measured.
There is some debate about whether very low cholesterol is bad. Low cholesterol is often seen when there is an existing problem like malnutrition, liver disease, or cancer. However there is no evidence that low cholesterol causes any of these problems.
Cholesterol is high during pregnancy. 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 to a moderate extent, include oral corticosteroids, beta blockers, oral contraceptives, thiazide diuretics, oral retinoids and phenytoin.
Familial hypercholesterolaemia (FH) is a severe form of elevated cholesterol levels that runs in families. It is often undetected until damage is done and the person develops cardiovascular disease. It can be easily screened for and treated early in life. Information about FH can be found at the FH Australia network site. Individual risk of having FH can be determined using their online calculator.
High cholesterol may be the result of an inherited disease or it may result from an unhealthy diet (high in saturated and trans fats, and cholesterol) and lack of exercise. For many people it is caused by a combination of these modifiable factors and an inherited tendency towards high cholesterol.
Lifestyle factors should be managed at all risk levels. Healthy diet and other positive lifestyle changes, e.g. increased physical activity, smoking cessation, weight reduction, are quite important. Very high and resistant cholesterol levels need medication. Sometimes two different drugs are used together to treat people with extremely high cholesterol levels. The drug of choice differs for different people. There are several classes of drugs that are commonly used. These include bile acid sequestrants, niacin, HMG-CoA reductase inhibitors (statins) and fibrates. Your doctor will need to take into account your individual situation before prescribing any cholesterol-lowering drug.
High cholesterol increases your risk of a heart attack. The higher the cholesterol, the higher the risk. However, many other factors also affect your risk of a heart attack, such as gender, smoking, diabetes, age, and high blood pressure. Charts to allow you to assess your risk of a heart attack are available from the National Heart Foundation.
Cholesterol levels fluctuate over time. The measured cholesterol level may differ by as much as 10% from one month to another. It may go up sometimes or it may go down sometimes. These changes are called biological variation and they represent normal variability inherent in human metabolism.
Cholesterol levels fluctuate over time. A single measurement of cholesterol may not always reflect the ‘usual’ cholesterol level. For this reason, it is advisable to have at least two different measurements several weeks to several months apart before beginning any kind of treatment.
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