What is a cholesterol test?

A cholesterol test is a blood test that measures your total blood cholesterol level and its components, which include levels of HDL ('good cholesterol') and LDL ('bad cholesterol)'. Together, the results are known as your 'blood lipid profile'. Knowing your cholesterol (lipid) levels helps your doctor to assess your overall heart health and see if any lifestyle changes or other treatment is needed.

What levels are measured?

The cholesterol blood test result will give levels of:

• high-density lipoprotein (HDL) cholesterol - 'good cholesterol'
• low-density lipoprotein (LDL) cholesterol - 'bad cholesterol' 
• triglycerides
• total cholesterol
• total cholesterol/HDL ratio.

These make up your 'blood lipid profile' - lipids are just another name for the fatty substances in the body and bloodstream.

Why is a cholesterol test useful?

The cholesterol test is not used to diagnose a disease. Instead, measuring cholesterol and knowing the levels of these lipids provides important information on your health and your long-term risk of heart disease and stroke. Together with other cardiovascular risk factors (such as blood pressure and bodyweight), your cholesterol results can give your doctor an overall picture of your health.

If the blood test results are not within normal limits (see table below), this 'early warning' allows you to make lifestyle changes and consider treatments to lower your future risk of heart attack and stroke. Making changes on the advice of your doctor can greatly alter your risk.

When and where do I go for the test?

Normally, your doctor will ask you to have the cholesterol test at the nearest community diagnostic laboratory, or the practice nurse may be able to take the blood sample.

If you have had recent surgery, a heart attack or been unwell (eg, influenza), it is better to wait at least six weeks before having the test done, for a more accurate result.

Pregnant women should wait at least six weeks after the baby is born to have cholesterol measured, as cholesterol is higher during pregnancy.

How is the cholesterol test carried out?

Some cholesterol tests can be conducted with a finger-prick blood sample, but more detailed testing requires a blood sample collected from a vein in the arm.

You will probably need to fast (go without food and most drink apart from water) for a specified period (usually at least eight hours) before taking the test. If so, you will be told in advance by your doctor or local laboratory and have your test done first thing in the morning, to minimise the inconvenience of fasting.

You should still be allowed to drink water and take your normal medications - do not stop taking these unless your doctor advises you to (eg, if the medications would interfere with the test result).

People taking blood-thinning medications (eg, aspirin or warfarin), or those with bleeding or clotting problems, should also inform the nurse or laboratory staff of this before the blood sample is taken.

Inform nurse or sample taker of any concerns

Some people feel nervous about having blood taken; however, the person taking the sample (your practice nurse or, at a laboratory, a person called a phlebotomist) is trained in this procedure, and it is usually straightforward.

If you have previously experienced problems having blood taken, inform the nurse or phlebotomist beforehand of any concerns you have, so they can attempt to minimise these.

How is the blood sample taken?

A band may be put around your upper arm to make the veins below expand and make it easier to draw blood from them. Your arm may feel tight for the short time the band is applied. The injection site will be cleaned with an alcohol swab.

You may feel a brief sting or pricking as the needle is inserted. A tube will be attached to the needle for collection. Your tests may require more than one vial of blood to be collected while the needle and tube is in place.

If you feel squeamish or nervous, it is often better not to watch. If you find yourself feeling faint or light-headed before, during or after the procedure, tell the nurse or phlebotomist and there should be the option for you to lie down. Similarly, if you have had this sort of reaction in the past, tell the nurse or phlebotomist in advance.

Interpreting the cholesterol test results

Your doctor will advise you of the results of the cholesterol tests and what these mean in relationship to your age, sex and general health profile. According to the New Zealand guidelines an ideal lipid profile is: 

• Total cholesterol less than 4 mmol/L *
• LDL cholesterol less than 2.0 mmol/L *
• HDL cholesterol greater than 1 mmol/L
• Total cholesterol/HDL ratio less than 4
• Triglycerides less than 1.7 mmol/L.

* Note: Lower targets are appropriate for people after a coronary artery bypass graft (CABG); your doctor will advise on target total cholesterol and LDL cholesterol values in this instance.

These cholesterol results are not interpreted on their own - your doctor will take other heart risk factors into account as well. If your cholesterol level is high, you should have regular check-ups every three to six months, depending on the results and your doctor's advice. 

What happens afterwards?

After the blood sample is taken, a cotton swab is applied to the site and held there for at least three minutes with a firm pressure. This will stop bleeding and help minimise any bruising. A plaster is applied, which can be removed after about half an hour.

Once leaving the practice/laboratory, you should avoid strenuous activity or heavy lifting with the arm for about one hour.

Some people develop a bruise at the injection site - some people bruise more easily than others. Any small bruise should fade after a few days.

Less common reactions to a blood test

Less often, there may be bleeding after the sampling, or a lump (called a haematoma) may develop at the injection site. If so, firm pressure should be applied for 10-15 minutes. A cold pack (eg, ice cubes in a plastic bag or wrapped in a cloth) can also reduce swelling.

The injection site may be tender and a more extensive bruise may develop from a haematoma. The bruise can take up to 10 days to go away, but there are no long term side effects from this. If you have any ongoing concerns after the procedure, contact your doctor or laboratory nurse.

Related topics

Also see: High blood cholesterol
Tackling your heart risk factors
Know Your Numbers Heart Age Calculator

Original content provided by everybody. Reviewed February 2011.