Scientists have found a blood marker that can indicate a person is at risk of developing rheumatoid arthritis even years before the debilitating condition occurs, they say.

About 1.3 million Americans have rheumatoid arthritis, known also as RA, an autoimmune disorder that causes chronic disease and pain and can also result in permanent disability. The key to preventing such damage is diagnosing and treating the disease early.

Now scientists at Oxford University say they’ve found a marker in the blood that can not only diagnose RA more accurately that current testing but can also predict who is at risk for the disease up to 16 years before the condition actually appears.

RA is the result of bodily inflammation. When such inflammation occurs, some proteins are altered in a process called citrullination. This prompts an immune response from the body, causing it to turn on itself, and in this case resulting in RA.

A certain form of protein antibody that occurs in RA is known as tenascin-C.  In a study of 2,000 patients, the researchers found that not only could the presence of tenascin-C in the blood help diagnose RA but it also could be found in people who developed the disease up to 16 years before it occurred.

This test could prove very useful in detecting the disease at its earliest stage, when treatment is most effective, the researchers said of the study, which appears in the Annals of Rheumatic Diseases.