Summary

• HDL-cholesterol is often termed ‘good’ cholesterol because it is known to protect you against atherosclerosis – a buildup of plaque in your arteries and blood vessels that can lead to heart disease and stroke. This is also known as cardiovascular disease or CVD.
• It is carried through the blood packaged up with proteins. Together they are called lipoproteins.
• There are different types of lipoproteins depending on the amounts of fat and protein they contain. These are termed high-density lipoprotein (HDL) and low-density lipoprotein (LDL).
• Apolipoprotein A-1 (Apo A-1) is found in high-density lipoprotein.
• By measuring the levels of Apo A-1 in your blood, it is possible to estimate the amount of HDL or ‘good’ cholesterol you have in your blood.

What are lipoproteins?

Cholesterol and triglycerides are fats and therefore cannot be dissolved in water. They need help to move through the blood, as blood is a liquid, and so are processed in the liver where they are packaged up with proteins into lipoproteins. This enables it to move through blood rather than rising to the top, like oil on water. In this way, they travel to organs and tissues where and when they are needed for energy or storage.      

There are different types of lipoproteins depending on the amounts of fat and protein they contain. They are termed high-density lipoprotein (HDL) and low-density lipoprotein (LDL). There are also different subtypes of lipoproteins such as very low-density lipoprotein (VLDL) and intermediate density lipoprotein (IDL). In general, lipoproteins with a higher fat content and lower protein content (lower density such as LDL and VLDL) are more likely to stick to artery walls and cause a buildup of plaques. 

What is Apolipoprotein A-1?

Apo A-1 is the main protein in high-density lipoprotein (HDL).

Cholesterol packed up in HDL, called HDL-cholesterol, is often termed ‘good’ cholesterol because it is known that people who have higher levels of HDL-cholesterol have a lower risk of heart disease and stroke. HDL-cholesterol plays a role in removing plaque from artery walls to be transported to the liver for disposal (reverse cholesterol transport). However, the degree to which it does this is unclear.

If your level of Apo A-1 is low, it means that you have a higher risk of developing atherosclerosis – a buildup of plaque in your arteries and blood vessels that can lead to heart disease or stroke.

It is important to note that Apo A-1 is different to apo(a) which is measured as part of the Lp(a) test. Apolipoprotein (apo) is a broad term that refers to any protein component of a lipoprotein. There are several types of apolipoproteins, including Apo A-1, Apo B, Apo C, and Apo E, each with specific roles in lipid metabolism.

• Apo A-1 is the main apolipoprotein in HDL and protects you from cardiovascular disease.
• Apo(a) is a different apolipoprotein that is part of Lp(a) and increases the risk of plaque buildup.

Why get tested?

Measuring Apo A-1 tells your doctor the amount of HDL in your blood. Another test, HDL-cholesterol (HDL-C) measures the cholesterol content within the HDL particles.

This difference is important: the number of HDL particles can be a better indication of CVD risk than the amount of cholesterol they carry. This means that measuring Apo-A1 can be better than the HDL-cholesterol test in measuring your CVD risk.

Levels of Apo A-1 tend to rise and fall with HDL levels, and deficiencies in Apo A-1 correlate with an increased risk of developing CVD.

Apo A-1 is not used routinely but may be helpful if you have already had a lipid profile test that shows you have high levels of lipids in the blood (hyperlipidaemia). It may also be used if you have a family history of heart disease, high cholesterol levels or heart disease, particularly if family members have had heart attacks at a relatively young age.

It may be requested along with an apolipoprotein B-100 (Apo B) level if your medical team wants to check your Apo A/Apo B ratio. This shows the ratio of ‘good’ to ‘bad’ cholesterol.

The Apo A-1 test is also used to help diagnose rare conditions that cause Apo A-1 deficiencies, such as Tangier and Fisheye disease.

If you are having lipid lowering treatment, an Apo A-1 test may be ordered along with other tests, to see if the level of cholesterol and fat in your blood is improving.

Having the test

Sample

Blood.

Any preparation?

Fasting is generally not required for an Apo A-1 test so a non-fasting sample is considered suitable. However, it's always a good idea to confirm with your doctor, as some requirements may vary.

Your results

Reading your test report

Your results will be presented along with those of your other tests on the same form. You will see separate columns or lines for each of these tests.

A low level of Apo A-1 in the blood means you likely have a low level of HDL, the ‘good’ cholesterol. This suggests your body is not getting rid of excess cholesterol very well and may increase your chance of developing CVD.

Low Apo A-1

A low level of Apo A-1 in the blood may be due to inheriting a genetic condition such as familial hypoalphalipoproteinaemia but this is rare, and most often, low Apo A-1 is due to:

• chronic kidney failure,
• some medications, including androgens, beta blockers, diuretics, and progestins, 
• smoking, or
• poorly managed diabetes.

High Apo A-1

A high level of Apo A-1 in the blood is usually not a problem. It may run in the family. More commonly, Apo A-1 may be increased due to:

• medications used to treat hyperlipidaemia, such as lovastatin, simvastatin, and niacin,
• other medications such as carbamazepine and oestrogens (including oral contraceptives),
• physical exercise,
• pregnancy, or
• weight loss.

Women often have higher HDL, and so also tend to have higher levels of Apo A-1.

More to know

The Apo A-1 test is not routinely used. Doctors and scientists still have to determine the best uses for Apo A-1. It may provide your medical team with additional information in specific situations but does not replace the lipid tests routinely available.

Questions to ask your doctor

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods, medications or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

More information

Pathology and diagnostic imaging reports can be added to your My Health Record.

You and your healthcare provider can now access your results whenever and wherever needed. Get further trustworthy health information and advice from healthdirect.