What is this test used for? 
APOE is a genotype (genetic) test. This test is to detect the presence of the APOE4 variant, which is associated with increased risk of  Alzheimer's disease (AD). Testing may be considered for patients with dementia to supplement information from clinical and other evaluations. This test is not appropriate for children.
 
Use
Alzheimer's disease is a progressive neurodegenerative disorder that affects more than 6.7 million Americans ages 65 and older and is the most common form of dementia in the elderly. Signs and symptoms may include cognitive decline, memory loss, loss of problem-solving skills and personality changes. Clinical symptoms appear after 60-65 years in 95% of cases. The development of late-onset disease may be influenced by age, sex, family history, level of education, history of head trauma and other factors including cardiovascular risk factors. Approximately 15-20% of late-onset disease may be familial. The APOE gene is a known susceptibility gene for Alzheimer's disease. The APOE gene encodes apolipoprotein E, which has a role in lipid metabolism. APOE has three common alleles: E2, E3 and E4. The presence of the E4 allele increases the lifetime risk of Alzheimer's disease but is neither necessary nor sufficient for the development of Alzheimer's disease. APOE E2 may have some protective effect against development of late-onset disease.1 APOE also has a rate allele: E1 (legacy name E3r). There is insufficient evidence to assess the clinical association of APOE E1 with Alzheimer's disease.2