What APOE Testing Can and Can't Do
A blood test is available that can identify which APOE alleles a person has. However, because the APOE e4 gene is only a risk factor for Alzheimer's disease, this blood test cannot tell whether a person will develop Alzheimer's disease or not. Instead of a yes or no answer, the best information a person can get from this genetic test for APOE is maybe or maybe not. Although some people want to know whether they will get Alzheimer's disease later in life, this type of prediction is not yet possible. In fact, some researchers believe that screening measures may never be able to predict Alzheimer's disease with 100% accuracy.
In a research setting, APOE testing may be used to identify study volunteers who may be at a higher risk of getting Alzheimer's disease. Researchers can look for early brain changes in these patients. This test also helps researchers compare the effectiveness of treatments for patients with different APOE profiles. Most researchers believe that the APOE test is useful for studying Alzheimer's disease risk in large groups of people, but not for determining one person's individual risk. Predictive screening in otherwise healthy people will be useful if an accurate/reliable test is developed and effective ways to treat or prevent Alzheimer's disease become available.
In diagnosing Alzheimer's disease, APOE testing is not a common practice. The only definite way to diagnose Alzheimer's disease is by viewing a sample of a person's brain tissue under a microscope to determine if there are plaques and tangles present. This is usually done after the person dies. However, through a complete medical evaluation (including a medical history, laboratory tests, neuropsychological tests, and brain scans), well-trained doctors can diagnose Alzheimer's disease correctly up to 90% of the time. Doctors look to rule out other diseases and disorders that can cause the same symptoms of Alzheimer's disease. If no other cause is identified, a person is said to have "probable" or "possible" Alzheimer's disease. In some cases, APOE testing may be used in combination with these other medical tests to strengthen the diagnosis of a suspected case of Alzheimer's disease. Currently, there is no medical test to establish if a person without the symptoms of Alzheimer's disease is going to develop the disease. APOE testing as a patient screening (predictive) method is not recommended.
(Click Symptoms of Alzheimer's for more information about the symptoms of this disease.)