Summary

• LDL-cholesterol is often termed ‘bad’ cholesterol because it increases the risk of 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.
• Cholesterol and another form of fat, called triglycerides, are 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). There are also subgroups such as very low-density lipoprotein (VLDL), intermediate density lipoprotein (IDL) and chylomicrons.
• Apo B-100 is a protein that is part of every very low-density (VLDL), intermediate density lipoprotein (IDL) and low-density lipoprotein (LDL). This makes measuring Apo B-100 a very useful way of assessing the amount of non-high-density lipoproteins in your blood.

What are lipoproteins?

Cholesterol and triglycerides are types of fats, also called lipids, that are essential for many of your body’s functions. They cannot be dissolved in water and so they need help to move through the blood, as blood is a liquid. They are processed in the liver where they are packaged with proteins into lipoproteins. This enables them 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.  

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), intermediate density lipoprotein (IDL) and chylomicrons.

In general, lipoproteins with a higher fat content and lower protein content (e.g. lower density such as LDL and VLDL) are more likely to stick to artery walls and cause a buildup of plaques.

When you have high amounts of cholesterol and triglycerides circulating in your blood packaged up in low-density lipoprotein, they stick together with other fats, cells, calcium and debris floating around in the bloodstream and form plaques in the walls of arteries. The buildup of plaque narrows the space within the artery.  

Although lipids are essential for many of your body’s functions, having too much of low-density types of lipoproteins in your blood is harmful. Your body has systems in place for getting rid of excess lipids but sometimes these systems don’t work as they should, or they become overloaded. Some people inherit conditions that cause them to have too much low-density lipoproteins.

What is Apo B-100

Apo B-100 is a protein that is part of very low-density (VLDL), intermediate density lipoprotein (IDL) and low-density lipoprotein (LDL). It helps the lipoproteins to find and be taken up by the cells in your body that need cholesterol.

Each LDL, VLDL and IDL contains exactly one Apo B-100 particle, making measuring Apo B-100 a useful way to assess the amount of non-high-density lipoproteins in your blood. For more on lipoproteins and how they are made see Lipid Profile.

Why get tested?

If you have been asked to have an Apo B-100 test it is most likely that you have a history of high levels of LDL-cholesterol (cholesterol packaged up in low density lipoproteins), or a family history of cardiovascular disease (CVD). You will have already had results from a Lipid Profile test that shows you may be at risk of CVD.

Apo B-100 testing is not used as a general population screen but is usually ordered when someone has high triglyceride levels which makes calculating LDL cholesterol results from the lipid profile more difficult and reduces accuracy.

Occasionally, an Apo B-100 test is used to help diagnose a genetic problem that causes over- or under-production of Apo B-100.

High Apo B-100 levels can be due to a genetic change or mutations in the Apo B gene. This mutation can mean that the Apo B your body produces does not work properly and as a result the lipoproteins cannot find and deliver cholesterol to cells.  This causes blood cholesterol levels to be high.

This is one of the causes of Familial Hypercholesterolaemia (FH). More commonly, FH is due to a genetic mutation of the LDL receptor gene. This is the gene that allows the cells in your body to find and take cholesterol from lipoproteins. Genetic mutations in this gene slows the clearing of LDL from the blood.

Sometimes doctors will order both Apo A (associated with high-density lipoprotein (HDL) - the 'good' cholesterol) and Apo B-100 levels to get a ratio of Apo B and Apo A. This helps in assessing CVD risk.

Elevated levels of Apo B-100 are associated with a higher number of lipid particles (like LDL, VLDL, and IDL) in the blood that can contribute to the development of atherosclerosis and increase the risk of cardiovascular diseases such as heart attacks and strokes.

Occasionally, Apo B-100 levels may be ordered to monitor the effectiveness of lipid treatment like statins. A decrease in Apo B-100 levels indicates that the treatment is successfully lowering plaque forming lipids.

Apo B-100 levels can be useful in diagnosing patients with complex lipid disorders.

When LDL cholesterol levels are controlled, patients can still have a high number of plaque forming lipids. Measuring Apo B-100 provides additional information on cardiovascular risk.

In rare cases, they may be measured to help diagnose a genetic problem that causes over- or under-production of Apo B-100.

Having the test

Sample

Blood.

Any preparation?

A fasting sample is generally recommended for an Apo B-100 test. However, some doctors accept that a non-fasting sample can be used. It's always best to follow the specific instructions provided by your doctor or the laboratory conducting the test.

• Fasting Lipid Testing: You need to fast for 8-12 hours before the test, meaning you should not eat or drink anything except water before the blood sample is taken. Fasting means that recent food intake does not affect your test results, providing a more accurate measurement of your lipid levels.
• Random Lipid Testing: This test does not require fasting, so you can eat and drink normally before the test. More recent studies show that random (non-fasting) lipid testing can provide accurate results, and it is more convenient and safer for people with diabetes as they do not have to fast.

Your results

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.  

High levels of Apo B-100 reflect high levels of LDL-cholesterol and an increased risk of CVD. High levels may be due to a high fat diet and/or problems in clearing of LDL-cholesterol from the blood such as when you have a genetic mutation. Increased levels of Apo B-100 are seen with hyperlipidaemia and conditions such as:

• Diabetes
• Familial hypercholesterolaemia
• Familial combined hyperlipidaemia (an inherited disorder causing high blood levels of cholesterol and triglycerides)
• Hypothyroidism
• Nephrotic syndrome (a kidney disease)
• Pregnancy (levels increase temporarily and decrease again after delivery)

Apo B-100 levels may be decreased with any condition that affects lipoprotein production or affects its synthesis and packaging in the liver. Lower levels are seen with:

• Drugs such as: oestrogen (in post-menopausal women), lovastatin, simvastatin, niacin, and thyroxine
• Diet: Vegans have lower levels of Apo B-100 than meat eaters
• Hyperthyroidism
• Malnutrition
• Weight reduction
• Severe illness
• Surgery
• Familial hypobetalipoproteinaemia and abetalipoproteinaemia
• Cirrhosis

A high ratio of Apo B-100/Apo A may indicate a higher risk of developing coronary artery disease.

More to know

There are two forms of apolipoprotein b: Apo B-100 and Apo B-48. Apo B-48 is created in the intestines. It is an integral part of the structure of chylomicrons, large lipoproteins that are responsible for moving lipids through your blood. Laboratory tests typically do not measure Apo B-48 and only measure Apo B-100.

While researchers are looking into the role of chylomicrons (the lipoprotein that contains Apo B-48), at present there is no clinical advantage in measuring Apo A-48.

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.