Apolipoprotein E

Apolipoprotein E blood test measures the amount Apolipoprotein E in the blood. This test helps to determine the risk of heart diseases and Alzheimer’s disease (AD).

What is Apolipoprotein E?

Apolipoprotein E is a fat-binding protein present in the body. It is the main protein component of chylomicrons, and intermediate-density lipoprotein (IDL). Apo E is mainly produced by the liver and helps in cholesterol breakdown. It is also produced by astrocytes (nerve cells) and known as the primary cholesterol carrier in the brain.

Lipids cannot dissolve in blood by itself. Apolipoproteins combine with lipid to form lipoproteins and help in the transport of lipids throughout the bloodstream. Lipoproteins are spherical in structure and are of four (4) types. Each type of lipoprotein has its own characteristic protein and lipid composition. They are the high-density lipoprotein (HDL), low-density lipoprotein (LDL), very low-density lipoprotein (VLDL), and chylomicrons.

Apolipoprotein E helps in the lipoprotein breakdown (Lipoprotein Metabolism). Inadequate levels of Apo E may increase the levels of cholesterol and triglycerides in the blood. This may lead to the risk of developing heart diseases.

In the nervous system, Apo E is involved in the production, degradation, and removal of Amyloid Beta. It is a protein involved in neural growth and repair. If this protein is not properly degraded or removed it clumps into plaques that lead to nerve cell death. Overproduction or failure of clearance of amyloid beta can lead to a neurogenerative disorder called Alzheimer's disease (AD). An AD is the most common type of dementia that results in problems with memory, thinking, and behavior. If the astrocytes are not producing sufficient levels of Apo E it may disrupt the normal function of amyloid beta.

Assessing the levels of Apolipoprotein E reflects the risk of cardiovascular diseases (heart diseases) and Alzheimer’s disease (AD). Therefore low levels than the normal range of Apolipoprotein E in the blood may increase the risk of cardiovascular diseases (heart diseases) and Alzheimer’s disease (AD).

Why this test is performed?

This test is performed to determine whether you have normal or abnormal levels of Apolipoprotein E in the blood. Your doctor may ask to perform this test if you have a family history of cardiovascular diseases or if you are at risk of developing cardiovascular diseases. You may be advised to perform this test to diagnose the cause of abnormal lipid levels, especially when someone has elevated triglyceride levels.

This test is also performed if you have a family history of Alzheimer’s disease (AD) or if you experience any signs and symptoms of Alzheimer’s disease (AD) such as difficulty in remembering newly learned information, problems with thinking or behavior, forgetting events, misplacing personal belongings, inability to recognize people, impaired speaking, reading or writing, etc.

How often this test is performed?

If you have a family history of cardiovascular diseases (heart diseases) or Alzheimer’s disease (AD) your doctor may ask to perform this test in a 6 monthly or a yearly basis. If you are diagnosed with cardiovascular diseases (heart diseases) and/or Alzheimer’s disease (AD) then you may have to perform this test on a regular basis as instructed by the doctor.

If the test results show low levels of Apo- E than the normal range it may indicate the risk of cardiovascular diseases. Individuals with an inherited disorder called familial apolipoprotein (apo) E deficiency (a condition where Apo E is absent) may also show decreased or no Apo-E levels in the blood. Low levels of Apo-E may lead to a condition called hypertriglyceridemia (High levels of triglycerides in the blood).

Decreased levels of Apo-E may also indicate the risk of Alzheimer’s disease (AD). However, your doctor may ask to perform a few more additional tests along with this test to confirm the diagnosis.

High levels of Apo-E in the blood is not very common. Based on the test results, your doctor may advise appropriate medical treatments, lifestyle modifications, or further diagnostic tests.