Apolipoprotein B, also called ApoB, is a protein found on some cholesterol and fat-carrying particles in the blood. These particles can enter artery walls and contribute to plaque buildup, which can increase the risk of heart attack and stroke.
The ApoB test measures the number of these artery-clogging particles more directly than LDL cholesterol alone. This can be especially useful when LDL cholesterol looks normal but heart disease risk may still be high.
Apolipoprotein B levels may be higher in people with high triglycerides, diabetes, obesity, metabolic syndrome or certain inherited cholesterol disorders. Levels can often be lowered with lifestyle changes and, when needed, cholesterol-lowering medications.
What its function is
Apolipoprotein B helps carry fats, including cholesterol and triglycerides, through the bloodstream. It is found on several types of lipoproteins, which are particles that transport fats in the blood.
The main form measured in blood tests is ApoB-100. ApoB-100 is found on LDL, VLDL, IDL and lipoprotein(a), also known as Lp(a). These particles are considered atherogenic, which means they can contribute to plaque buildup in the arteries.
Each of these particles usually has one ApoB molecule. For this reason, an Apolipoprotein B test can help estimate the number of harmful cholesterol-carrying particles in the blood.
ApoB is different from ApoA-I, another apolipoprotein that is mainly found on HDL cholesterol. HDL cholesterol is often called “good” cholesterol because it helps remove cholesterol from the blood and take it back to the liver.
Why the ApoB test is done
The ApoB test is done to better understand a person’s risk of atherosclerotic cardiovascular disease. This includes conditions caused by plaque buildup in the arteries, such as coronary artery disease, heart attack and stroke.
This test may be especially useful when standard cholesterol tests do not fully explain cardiovascular risk. For example, ApoB may be ordered when LDL cholesterol is normal but triglycerides are high, or when a person has diabetes, obesity or metabolic syndrome.
Apolipoprotein B testing may also be useful in people who already have heart disease and need closer monitoring. It can help show whether treatment is lowering the number of harmful cholesterol particles, not just the amount of cholesterol inside them.
Doctors may also consider this test when there is a family history of early heart disease or suspected inherited cholesterol problems, such as familial combined hyperlipidemia.
Normal and high values
ApoB levels are usually measured in mg/dL. The meaning of the result can vary depending on age, sex, overall health and cardiovascular risk.
For people with a higher risk of heart disease, doctors may recommend lower ApoB goals. For example, some sources suggest aiming for below 100 mg/dL in high-risk people and below 80 mg/dL in very high-risk people.
ApoB results should not be interpreted alone. They are usually reviewed together with LDL cholesterol, HDL cholesterol, triglycerides, non-HDL cholesterol, blood pressure, blood sugar levels, smoking history, family history and other heart disease risk factors.
What causes high Apolipoprotein B?
High Apolipoprotein B usually means there are too many atherogenic particles in the blood. These particles can carry cholesterol into artery walls and raise the risk of plaque buildup.
Common causes and related conditions can be grouped into:
Cholesterol and triglyceride changes
ApoB can be high when LDL cholesterol or triglycerides are high. It can also be high when there are many small cholesterol-carrying particles in the blood, even if LDL cholesterol does not look very high.
Metabolic conditions
ApoB is often higher in people with obesity, insulin resistance, metabolic syndrome or type 2 diabetes. These conditions can change how the body processes fats and cholesterol.
Inherited cholesterol problems
Some inherited conditions, such as familial combined hyperlipidemia, can increase ApoB levels. These conditions may also be linked to a family history of high cholesterol or early heart disease.
Lifestyle factors
ApoB may be higher in people who eat a diet high in saturated fat, added sugar or excess calories, especially when combined with low levels of physical activity.
Existing cardiovascular disease
People with established cardiovascular disease may have high ApoB or may need lower ApoB goals, because the risk of future heart attack or stroke is higher.
High ApoB vs. high LDL
LDL cholesterol shows how much cholesterol is inside LDL particles. ApoB gives an idea of how many harmful cholesterol-carrying particles are in the blood.
This is important because LDL cholesterol can look normal even when ApoB is high. This means there may still be many particles that can enter the artery wall and contribute to plaque buildup.
ApoB may be especially useful in people with high triglycerides, diabetes, obesity or metabolic syndrome. It may also be useful when LDL cholesterol is normal but heart disease risk still appears higher than expected.
LDL cholesterol is still an important test, but ApoB can give extra information about cardiovascular risk.
How to lower Apolipoprotein B levels
Apolipoprotein B levels can often be lowered by reducing the number of LDL, VLDL and other atherogenic particles in the blood. This may involve lifestyle changes, medication or both.
1. Lifestyle changes
Lifestyle changes may help lower ApoB, especially when they also improve LDL cholesterol, triglycerides, weight and insulin resistance. These changes may include eating less saturated fat, which is found in foods like fatty meats, butter, cream and full-fat dairy.
It may also help to limit trans fats, highly processed foods, added sugar and refined carbohydrates, especially when triglycerides are high. A heart-healthy eating pattern can include more fiber-rich foods, such as vegetables, fruits, beans, lentils, oats and whole grains, as well as unsaturated fats from foods like olive oil, nuts, seeds and fish.
Regular physical activity, weight loss when appropriate, avoiding smoking and limiting alcohol can also help improve overall cardiovascular risk. These habits may support healthier cholesterol and triglyceride levels over time.
2. Medications
When lifestyle changes are not enough, medications may be recommended to lower ApoB-related risk. Statins are the most commonly used medicines, as they help reduce LDL particle production and help the liver remove LDL particles from the blood.
Other treatment options may include ezetimibe, PCSK9 inhibitors, bile acid sequestrants or fibrates, especially when triglycerides are high. The best treatment depends on overall cardiovascular risk, cholesterol results, medical history and how well the medication is tolerated.
Studies have shown that lowering ApoB through lipid-lowering treatment is linked with lower cardiovascular risk.
When to see a doctor
A doctor should be consulted when ApoB is high, especially if there are other cardiovascular risk factors. These include high blood pressure, diabetes, smoking, obesity, high triglycerides, kidney disease or a family history of early heart disease.
Medical evaluation is also important if LDL cholesterol appears normal but cardiovascular risk remains unclear. In this situation, ApoB can provide extra information about the number of harmful particles in the blood.