Apolipoprotein E (Apo E) Genotyping

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Also known as: APOE Cardiac Risk
Formal name: Apolipoprotein E Genotyping

At a Glance

Why Get Tested?

To help confirm a diagnosis of Type III hyperlipoproteinaemia (also known as dysbetalipoproteinaemia, remnant disease or broad beta disease) and to evaluate a possible genetic cause of atherosclerosis. Outside of routine clinic practice e.g. for research purposes, it can be used to help confirm a diagnosis of late onset Alzheimer’s Disease (AD) in a symptomatic adult

When to Get Tested?

This is a non-standard test currently limited mostly to hospital specialists. It can be measured if your doctor suspects that your high cholesterol and triglyceride concentrations may be due to a genetically inherited disorder, or if you have specific types of xanthomas (yellowish raised patches) on your skin (particularly palms, knees and elbows).

Sample Required?

A blood sample taken from a vein in your arm

Test Preparation Needed?

None; however this test is often requested at the same time as other tests that require fasting (water only), so you may be instructed to fast for 12 hours prior to having this test.

The Test Sample

What is being tested?

There are two methods to determine your apolipoprotein E (apo E) type. The test can look at a patient's DNA to determine what combination of apo E gene alleles (copies) he or she has. The apo E gene exists in three different forms – e2, e3, and e4 – with e3 being the most common form and considered to be 'neutral'. Everyone has a pair of apo E genes that is some combination of these three, for example e3/e3, e2/e2, e2/e4 etc.

An alternative method is based on electrophoresis as the proteins have different charges. Due to analytical limitations and the presence of rarer types/mutations one test may find abnormalities that the other misses. 

aApo E is made in the liver and brain and helps transport lipids (fats) from one place to another thus helping to clear dietary fats, such as triglycerides, from the blood.

The e2 form of apo E is less able to clear lipids from the blood compared to the other forms. This means that if someone has an e2/e2 combination, they may clear dietary fat from their body at a slower rate and be at a higher risk for early vascular disease because of the increased likelihood that the fats will be deposited in the blood vessel walls. It is not a straightforward diagnosis, however, as other factors, such as obesity, diabetes, and hypothyroidism, may play a role in whether a patient actually develops disease. 

The apo e4 allele has been shown to be associated with an increased risk of late onset Alzheimer's Disease (developing after the age of 65). While one copy of e4 constitutes a risk (e2/e4 or e3/e4) and two copies of e4 (e4/e4) indicate a greater risk of developing AD, the actual amount of risk involved has not been fully established, likely varies between individuals and has no role in routine clinical testing.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in your arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

None; however this test is often requested at the same time as other tests that require fasting (water only), so you may be instructed to fast for 12 hours prior to having this test.

The Test

Common Questions

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.