This Blood Test Could Predict Alzheimer's Disease 16 Years Before Symptoms Start

Symptoms of Alzheimer’s disease, like memory loss, confusion, personality changes and agitation, can show up as many as 10 years (or more) after the disease actually starts. But a new study found a blood test that could predict if someone will develop Alzheimer’s as many as 16 years before symptoms set in.

The study was published Monday in the journal Nature Medicine and looked at changes in the levels of a protein in the blood called neurofilament light chain (NfL). The protein demonstrates how much nerve cell loss you have in your brain — if you have more NfL in your blood, that means you have more brain damage.

Researchers studied 405 people enrolled in the Dominantly Inherited Alzheimer’s Network, an international research program for a rare form of Alzheimer’s caused by inherited gene mutations. People with the gene mutation typically develop Alzheimer’s before age 60 and have a 50-50 chance of passing on the mutation to their children.

Of the 405 people in the study, 243 carry the gene mutation and 162 are family members without the mutation. Researchers measured how their NfL levels changed, through blood samples, brain imaging and cognitive tests, about every two and a half years over a period of seven years (the study is still ongoing).

What they found was that changing NfL levels were correlated with cognitive decline and brain shrinkage. In addition, researchers noted specific changes in a smaller group of 39 patients with the mutation two years after their first participation in the study. They found that people whose NfL levels had previously risen rapidly were more likely to show signs of brain atrophy and lowered cognitive abilities.

NfL levels overall were higher for people with the mutation that leads to Alzheimer’s six years before symptom onset. When researchers studied how NfL levels changed over time, they discovered that NfL levels’ rate of change allowed researchers to tell the difference between mutation carriers and non-mutation carriers as early as 16 years before estimated symptom onset.

Currently there is no single test to diagnose Alzheimer’s, and this NfL test is not yet approved by the FDA to diagnose or predict brain damage. However, a very similar test is already used to test for protein levels in the blood caused by other neurological conditions and injuries.

Though the test is not specific to Alzheimer’s (yet) — people with other kinds of brain damage will also have higher NfL levels — researchers hope the test will be used in clinical trials, helping scientists discover how effective new Alzheimer’s treatments are.

“I could see this being used in the clinic in a few years to identify signs of brain damage in individual patients,” said Brian Gordon, one of the study’s authors. “We’re not at the point we can tell people, ‘In five years you’ll have dementia.’ We are all working toward that.”