Yes, blood tests can identify genes linked to Alzheimer’s disease. The most common test looks for variants of a gene called APOE, which comes in three forms: e2, e3, and e4. Carrying the e4 variant is the strongest known genetic risk factor for Alzheimer’s, though it doesn’t guarantee you’ll develop the disease. These tests are available through doctors and, in a more limited form, through consumer genetic testing services like 23andMe.
It’s also worth knowing that a different kind of blood test now exists, one that doesn’t look at your genes at all but instead detects proteins in your blood that signal Alzheimer’s-related brain changes. Both types of tests serve very different purposes, and understanding the difference matters.
The APOE Gene Test
The gene most commonly tested in relation to Alzheimer’s risk is APOE, located on chromosome 19. Everyone inherits two copies, one from each parent, and each copy comes in one of three common variants: e2, e3, or e4. The e3 variant is the most common and considered neutral. The e2 variant may offer some protection. The e4 variant raises risk.
The numbers are striking. People with no e4 copies have roughly a 20% lifetime risk of developing Alzheimer’s. Carrying one copy of e4 raises that to about 47%. Carrying two copies (one from each parent) pushes lifetime risk to approximately 91%. But these are population-level statistics. Plenty of people with one or even two copies of e4 never develop Alzheimer’s, and many people who get the disease carry no e4 at all.
The test itself is straightforward. A lab draws blood and uses a DNA-based technique to identify which APOE variants you carry. It’s listed under a specific billing code that covers testing related to cardiovascular disease, cholesterol disorders, and Alzheimer’s. Your doctor can order it, and results typically report your genotype as a combination like e3/e4 or e4/e4.
Rare Genes That Cause Alzheimer’s Directly
APOE e4 increases risk, but three other genes can actually cause Alzheimer’s with near certainty. Mutations in APP (discovered in 1987), Presenilin-1 (identified in 1992), and Presenilin-2 (discovered in 1993) are responsible for dominantly inherited Alzheimer’s, which typically strikes earlier in life, often before age 65. Presenilin-1 mutations are the most common cause of this inherited form.
Testing for these mutations is generally reserved for people with a strong family history of early-onset Alzheimer’s. It’s done in clinical settings with genetic counseling, not through consumer kits. If multiple family members developed Alzheimer’s in their 40s or 50s, this is the type of testing a specialist might recommend.
Consumer Genetic Tests vs. Clinical Tests
Services like 23andMe offer APOE testing as part of their health reports, which means you can learn your APOE status without a doctor’s order. The genetic information itself is the same: you’ll find out whether you carry e2, e3, or e4 variants. But the experience around getting that result is very different.
Clinical genetic testing typically involves a conversation with a genetic counselor before and after results come in. That matters because learning you carry one or two copies of APOE e4 can be emotionally significant. Research conducted within clinical settings, where genetic counselors are involved, has found that serious psychological distress from APOE disclosure is rare. But less is known about how people cope when they get these results through a consumer test, alone at their computer, without professional context.
APOE testing has also taken on a new practical role. Newer Alzheimer’s treatments that target amyloid plaques in the brain carry a risk of side effects involving brain swelling or bleeding, and that risk is higher for people with the e4 variant. Doctors now use APOE testing to help guide treatment decisions for patients considering these therapies.
Blood Tests That Detect Alzheimer’s Proteins
Separate from genetic testing, there’s now an FDA-cleared blood test that detects whether Alzheimer’s-related changes are happening in your brain right now. This is not a gene test. Instead, it measures specific proteins in your blood: a form of tau protein called p-tau217 and a fragment of amyloid, the sticky protein that builds up into plaques in Alzheimer’s.
In early 2025, the FDA cleared the first blood-based diagnostic test for Alzheimer’s disease. Made by Fujirebio Diagnostics, it measures the ratio of p-tau217 to a specific amyloid fragment and is designed for adults 55 and older who are already showing signs of cognitive trouble. In clinical studies, plasma p-tau217 showed about 82% to 83% sensitivity for detecting the hallmark brain changes of Alzheimer’s, with specificity around 83% to 86%. That means it correctly identifies most people who have amyloid or tau buildup, while also correctly ruling out most people who don’t.
This is a big deal because previously, confirming Alzheimer’s-related brain changes required either a PET scan (which can cost several thousand dollars) or a spinal tap to analyze cerebrospinal fluid. A blood draw is faster, less invasive, and expected to cost less than either of those options, though insurance coverage varies by carrier and plan.
How to Get Tested
For the APOE gene test, your primary care doctor or a specialist can place the order. Some people pursue it out of curiosity about their risk profile, others because a family history of Alzheimer’s has them concerned, and increasingly, patients are tested before starting certain Alzheimer’s medications. If your family has a pattern of early-onset Alzheimer’s, ask about testing for the rarer APP, Presenilin-1, and Presenilin-2 mutations as well.
For the newer protein-based blood test, the process is similar. A primary care physician or specialist orders the test, you visit a lab for a standard blood draw, and the sample is sent to a centralized facility with the specialized equipment to analyze it. This test is meant for people already experiencing memory or thinking problems, not as a screening tool for healthy adults.
One important distinction: the gene test tells you about inherited risk you’ve carried since birth. The protein test tells you whether disease-related changes are actively present in your brain. You could carry two copies of APOE e4 and show no amyloid buildup, or you could have no genetic risk factors and still test positive for brain changes. The two tests answer fundamentally different questions, and depending on your situation, one or both might be relevant.