A newly developed blood test for Alzheimer’s has diagnosed the disease as accurately as methods that are far more expensive or invasive, scientists reported on Tuesday, a significant step toward a longtime goal for patients, doctors and dementia researchers. The test has the potential to make diagnosis simpler, more affordable and widely available.

The test determined whether people with dementia had Alzheimer’s instead of another condition. And it identified signs of the degenerative, deadly disease 20 years before memory and thinking problems were expected in people with a genetic mutation that causes Alzheimer’s, according to research published in JAMA and presented at the Alzheimer’s Association International Conference.

Such a test could be available for clinical use in as little as two to three years, the researchers and other experts estimated, providing a readily accessible way to diagnose whether people with cognitive issues were experiencing Alzheimer’s, rather than another type of dementia. A blood test like this might also eventually be used to predict whether someone with no symptoms would develop Alzheimer’s.