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ApoE Genotyping

Formally known as: Apolipoprotein E genotyping
Related tests: Cardiac Risk Assessment, HDL Cholesterol, LDL Cholesterol, Lipid Profile, Triglycerides, Tau/Aß42
The Test
 
How is it used?
When is it ordered?
What does the test result mean?
Is there anything else I should know?

How is it used?
ApoE genotyping is sometimes used as part of follow-up testing if high cholesterol and triglyceride levels are found, to check for and help diagnose a genetic component to a lipid abnormality. It is not widely used, but when it is ordered, it may be in combination with other tests, such as lipoprotein electrophoresis.

ApoE genotyping is also sometimes used as an adjunct test to help confirm a diagnosis of probable late onset Alzheimer’s Disease in symptomatic adults. It is called susceptibility or risk factor testing because it indicates whether there is an increased risk of AD but is not diagnostic of AD. There are no clear-cut tests to diagnose Alzheimer’s Disease; the best a doctor can do right now is to rule out anything else that may be causing dementia and check for a genetic predisposition to AD (with ApoE genotyping, perhaps in conjunction with Tau/Aß42 testing).



When is it ordered?
ApoE genotyping is sometimes ordered when a patient has significantly elevated cholesterol and triglyceride levels that do not respond to changes in the patient’s lifestyle (dietary and exercise patterns); when a patient presents with xanthomas (yellowish lesions) on their skin and the doctor suspects Type III hyperlipoproteinemia; or when family members have ApoE e2/e2 and a doctor wants to see if the patient may be at a higher risk for early heart disease.

ApoE genotyping is also sometimes ordered as an adjunct test when patients have symptoms of progressive dementia, such as decreasing intellectual ability and language and speech skills, memory loss, and personality and behavioral changes that are starting to interfere with daily living. After non-AD causes, such as overmedication, vascular dementia (caused by strokes), and thyroid disease, have been ruled out, ApoE genotyping may help establish a diagnosis of probable Alzheimer’s Disease.



What does the test result mean?
Patients with ApoE e2/e2 alleles are at a higher risk of premature vascular disease, but they may never develop disease. Likewise, they may have the disease and not have e2/e2 alleles because it is only one of the factors involved. ApoE genotyping adds additional information and, if symptoms are present, e2/e2 is diagnostic of Type III hyperlipoproteinemia (although diagnosis must be made in conjunction with other test results and the patient’s clinical history).

Patients who have ApoE e4/e4 are more likely to have atherosclerosis. Patients who have symptoms of late onset Alzheimer’s Disease AND have one or more ApoE e4 copies of the e4 gene are more likely to have AD. It is not diagnostic of AD, though, and should NOT be used to screen asymptomatic patients or their family members. Many people will have e4 alleles and never develop AD. Even in symptomatic patients, only about 60% of those with late onset AD will have ApoE e4 alleles.

PLEASE NOTE: Numerically reported test results are interpreted according to the test's reference range, which may vary by the patient's age, sex, as well as the instrumentation or kit used to perform the test. A specific result within the reference (normal) range – for any test – does not ensure health just as a result outside the reference range may not indicate disease. To learn more about reference ranges, please see the article, Reference Ranges and What They Mean. To learn the reference range for your test, consult your doctor or laboratorian. Lab Tests Online recommends you consult your physician to discuss your test results as a part of a complete medical examination.



Is there anything else I should know?
Although ApoE genotyping is being used clinically by Alzheimer’s experts, the most it can provide at this time is additional information about a patient with dementia. A definite diagnosis of Alzheimer’s Disease can only be made by examining a patient’s brain tissue after their death.

ApoE genotyping is not available in every laboratory. If your doctor recommends this test, your specimen will need to be sent to a reference lab and results may take longer to return than they would from other labs.




This page was last modified on May 16, 2002.
 
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