What Is the Apolipoprotein B-100 (ApoB) Test?

Medically Reviewed by Jabeen Begum, MD on October 12, 2023
3 min read

An ApoB test helps your doctor analyze whether or not you are at risk for heart disease. It measures the amount of apolipoprotein B in your blood. Apolipoprotein B attaches to negative types of cholesterol that cause plaque buildup in your blood vessels, which can lead to damage and heart disease.  

Apolipoprotein B-100 is a protein that helps carry fat and cholesterol through your body. It is also called apolipoprotein B or apoB, for short.

Your body needs fat and cholesterol to produce hormones and keep your cells healthy. Despite being necessary, fat and cholesterol don't dissolve well in the blood. In order for your body to deliver these compounds, they are packaged into a compound called a lipoprotein, with an apolipoprotein on the outside. 

ApoB carries a variety of lipoproteins, which are known as bad cholesterol:

  • Lipoproteins, like chylomicrons
  • Very-low-density lipoproteins (VLDL)
  • Low density lipoproteins (LDL)
  • Intermediate-density lipoproteins (IDL) . 

There are two types of apoB: apoB-48, which is made in your gut, and apoB-100, which is made in your liver. ApoB-48 carries fat and cholesterol to your liver, where it is repackaged and combined with apoB-100. From here, it moves throughout your body.

The apoB protein attaches to receptors on your cells, which allows the lipoprotein, or bad cholesterol, into the cell. Once inside, it’s broken down, releasing the fat and cholesterol into your blood. The bad cholesterol can cause plaque buildup in your blood vessels.

Healthy people have small amounts of low-density cholesterol in their blood, but higher numbers can mean you are at risk for heart problems. Since each of these cholesterol carries one apoB, the test is a good measure for the total amount of lipoproteins or bad cholesterol present in your blood. 

Your doctor might order this test for different reasons, including:

Your doctor might order other tests along with the apoB-100 test. They may include a lipid panel, which measures a variety of things: 

  • Cholesterol levels
  • Triglyceride levels
  • Existence of "good" cholesterol, or high-density lipoprotein
  • Low density lipoprotein (LDL) rates

 Your doctor might compare the lipid panel results with the apoB results to analyze your overall risk for heart disease. 

The apoB test is a simple blood test. A lab technician or nurse draws blood from your arm to use for analysis.  

If your doctor orders other tests, like a lipid panel, you may need to fast for 12 hours before your test. When fasting, it's important to drink only water. Your doctor will tell you if this is necessary.

The normal range for apolipoprotein B is less than 90 milligrams per deciliter, or mg/dL, of blood. If you receive normal test results, you have appropriate amounts of lipoproteins in your blood and your risk for heart disease is low.

Abnormal results can mean a few things. 

High levels of apoB. ApoB-100 levels measuring above 110 milligrams per deciliter are high. If your test results show a higher than normal rate, you have a higher than normal risk for heart disease. 

Some underlying conditions can cause high apoB levels, including:

Low levels of apoB. If your test results show that you have lower than normal lipoproteins in your blood, there may be some underlying condition that prevents your body from producing lipoproteins or apolipoproteins. These include:

  • Reye syndrome
  • Overactive thyroid
  • Malnutrition
  • Liver scarring, called cirrhosis
  • Severe sickness
  • Apolipoprotein B deficiency, a rare genetic condition known as Bassen-Kornzweig syndrome

Your doctor might also compare your apoB levels to levels of apoA in your blood. ApoA is an apolipoprotein that attaches to your good cholesterol. If you have more apoB than apoA, you might have a higher risk of heart disease. 

Besides the conditions that can cause low or high levels, other medications and lifestyle factors might affect your test results. These include:

  • Hormone drugs like androgens, estrogens, and progestins
  • Beta blockers
  • Diuretics
  • Thyroid medication
  • Statins
  • Vitamin B3
  • Surgery
  • Weight loss
  • High-fat diet
  • Certain supplements and herbs

Make sure to talk to your doctor about all medications or supplements you are taking before your test. Keep in mind that normal ranges of apoB can also vary by lab and region, by the method used, or by your gender, age, and health history. Talk to your doctor to learn more about what your specific results mean.