Apolipoprotein E (ApoE) test

Apolipoprotein E is a protein encoded by the APOE gene. It binds to fats (lipids) in the body and together with them forms lipoprotein particles — molecules that carry cholesterol and other fats in the blood. These particles transport cholesterol from one part of the body to another, and also help remove its excess from the blood. According to MedlinePlus, the APOE gene has three most common variants (alleles), called e2, e3 and e4. Each person inherits one allele from each parent, so everyone has a combination of two alleles. The e3 allele is the most common, found in more than half of the population, and is considered neutral. Because of this, laboratories most often carry out the apolipoprotein E test by determining which combination of alleles a person has, rather than only measuring the concentration of the protein in the blood — although some laboratories can also measure the concentration in mg/l. The result is usually assessed together with the lipid panel and family history.

• When there is a family history of unusually early cardiovascular disease, or of inherited disorders of lipid metabolism
• When a rare condition is suspected — type III hyperlipoproteinaemia (mixed hyperlipidaemia), in which both cholesterol and triglycerides are raised
• Together with the lipid panel, when LDL or triglyceride values are unusual and other causes have not been found
• Sometimes in the context of research or a specialised neurological consultation concerning the link between the e4 allele and late-onset Alzheimer's disease — the decision on whether such a test is appropriate is made by a doctor
• When assessing whether features of lipid metabolism in the family may be inherited

The ApoE test most often determines the type of allele (e2, e3 or e4) rather than the concentration alone. According to MedlinePlus, having the e4 allele is associated with a greater risk of atherosclerosis and of cardiovascular disease, and also with a greater risk of late-onset Alzheimer's disease and dementia with Lewy bodies. These links are population-level statistics, not a personal assessment.

• The presence of the e4 allele — MedlinePlus states a link with atherosclerosis and with the risk of cardiovascular disease
• The presence of the e4 allele — associated with a greater risk of late-onset Alzheimer's disease and dementia with Lewy bodies
• Coexisting disorders of lipid metabolism, because of which it is worth assessing the whole lipid panel

What to discuss with a doctor:

• The whole lipid panel (total cholesterol, LDL, HDL, triglycerides) for the overall picture
• Family history of early heart disease or dementia
• Whether genetic counselling is appropriate, after discussing the result with a doctor
• Lifestyle factors — diet, physical activity — which are worth discussing with a doctor

Causes of a decrease in the apolipoprotein E protein concentration are not widely described separately in reliable sources, and the genotype does not indicate the concentration — these are different tests. Separately, MedlinePlus states that having two copies of the e2 allele (the e2/e2 genotype) greatly increases the risk of a rare condition — type III hyperlipoproteinaemia — in which the removal of lipoprotein remnants from the blood is impaired.

• The e2/e2 genotype — MedlinePlus states that it greatly increases the risk of type III hyperlipoproteinaemia
• Impaired removal of lipoprotein remnants from the blood, associated with this rare condition

What to discuss with a doctor:

• The whole lipid panel, for an overall picture of lipid metabolism
• Genetic counselling, if an inherited condition of lipid metabolism is suspected
• Family history of unusual lipid disorders
• A discussion with a doctor about further monitoring