More than a million people in the United States have Parkinson's Disease.

Health experts say some people may not even know they have it. There's no cure for Parkinson's Disease, but researchers are trying to change that.

"There's really no definitive test in life to know whether someone has Parkinson's Disease, and so that really leads to a lot of uncertainty, but it also misdiagnosis unfortunately," Duke University School of Medicine Neurologist Laurie H. Sanders said.

Because there's been no definitive test, patients are left wondering for months, sometimes years, what's wrong.

But a team of neuroscientists at Duke University hope to change that.

They've developed a simple blood test that can precisely diagnose Parkinson's Disease, sometimes before symptoms start.

"We saw increases in our marker potentially decades before that they have the disease," Sanders said.

This test checks for damage inside the Mitochondria, which are the cells' energy centers. The test can tell with 85 percent accuracy whether someone has the disease.

"Our marker not only identifies Parkinson's patients, but those that might have some particular underlying biology that might match best with some drugs," Sanders said.

Leading to better treatments, sooner.

The next step for the blood test is to move it into larger clinical trials, with thousands of people, worldwide.

Researchers hope to make this test available to everyone within the next five years.