Alzheimer’s is a disease that can take over the brain long before cognitive symptoms manifest themselves. This is one of the main reasons why it is so difficult to diagnose the disease at its earliest stages. But a new experimental blood test may change that.

A novel blood test detected Alzheimer’s disease as accurately as expensive brain or spinal taps, raising the possibility for a new, inexpensive, and non-invasive option to diagnose the most common form of dementia.

Researchers at the Alzheimer’s Association International Conference on Tuesday presented the results of multiple studies of whether a blood test could distinguish Alzheimer’s disease from other forms of dementia.

In one of the published studies, researchers said the blood test could identify Alzheimer’s and even detected signs of the disease 20 years before cognitive problems were expected in a group of people who carry a rare genetic mutation.

What’s more, researchers reported the blood test measuring the protein tau – proteins that are typically abnormally shaped in the brains of people with Alzheimer’s – accurately distinguished Alzheimer’s from other forms of dementia in 89% to 98% of cases.

A blood test to detect Alzheimer’s early could be more precise than memory and thinking tests now used to diagnose the disease, which involves expensive brain scans and invasive spinal taps.

Randall J. Bateman, a Washington University neurology professor and Alzheimer’s researcher, said blood tests could be useful both for patients and doctors as well as scientists studying new drugs to slow the mind-robbing disease.

Doctors might use it to accurately diagnose Alzheimer’s earlier and begin treatments with existing Food and Drug Administration-approved drugs that ease symptoms, if not mental decline. But perhaps the bigger payoff would come for accelerating research for new drugs that seek to slow or halt a disease that afflicts 5.8 million older Americans.