The research, led by the University of Warwick in the UK, is published in the journal Scientific Reports.

The authors found that testing for citrullinated proteins (CPs) in the blood could lead to osteoarthritis (OA) being diagnosed years before physical symptoms emerge.

They also found that CPs may serve as a reliable way to detect early-stage rheumatoid arthritis (RA).

Lead researcher Dr. Naila Rabbani, reader of experimental systems biology at Warwick, says:

"This is a remarkable and unexpected finding. It could help bring early-stage and appropriate treatment for arthritis, which gives the best chance of effective treatment."

Dr. Rabbani and colleagues note that while there are established biomarker tests for early-stage RA, there are none for OA and suggest their findings could lead to a test for both that also distinguishes between the two.

CPs elevated in patients with early-stage OA, RA

Osteoarthritis is a joint disease associated with aging. It develops when the protective cartilage layer inside joints wears away because of continually being stressed over a person's lifetime. This type of arthritis normally affects the knees, hips, fingers and lower spine and rarely strikes before the age of 60.

The World Health Organization (WHO) estimate that about 9.6% of men and 18.0% of women over 60 have symptomatic osteoarthritis.

RA is a chronic systemic disease that affects not only the joints but also tendons, connective tissue, muscle and fibrous tissue. It is a disabling condition that often causes pain and deformity and tends to strike between the ages of 20 and 40.

According to WHO, RA affects up to 3% of the global population. The disease is more common in women and in developed countries, where around half of people who develop it are not able to have a full-time job within 10 years of onset.

For their study, the researchers developed a method based on mass spectrometry to measure CPs in body fluids. They found that CPs were elevated in patients with early-stage OA and early-stage RA.

Previous studies had already established that people with RA had antibodies to CPs, but these have not been found in early-stage OA.

Single blood test to detect and distinguish the two major forms of arthritis in early stages

In the next stage of their work, the team developed an algorithm that combined three biomarkers - CPs, anti-CP antibodies and hydroxyproline, a bone-derived compound - into one test.

Using the algorithm, they found that with a single blood test they could potentially detect and distinguish between the two types of arthritis before bone damage took place.

Dr. Rabbani explains that the algorithm uses the presence of autoimmunity to CPs in early-stage RA (antibodies are present) and the absence of such autoimmunity in early-stage OA (no antibodies) to distinguish between the two.

She explains that the team would have been satisfied with discovering the basis of a test for OA - but also finding they could discriminate between early-stage RA and other joint diseases was an added bonus:

"This discovery raises the potential of a blood test that can help diagnose both RA and OA several years before the onset of physical symptoms."

Meanwhile, Medical News Today recently reported how research is bringing closer the day when patients with knee osteoarthritis can benefit from stem cell therapy to regenerate damaged cartilage. In a study published inStem Cells Translational Medicine, researchers reported successfully regrowing cartilage in rats using embryonic stem cells.

Written by Catharine Paddock PhD