While blood tests are used to rule out other forms of arthritis, the diagnosis of osteoarthritis (OA) generally relies on physical symptoms, with X-rays or MRI scans used for conformation if required. But researchers at the University of Warwick in the UK have identified a biomarker for OA that could lead to a blood test that could diagnose it, and rheumatoid arthritis (RA), years before physical symptoms present themselves.

The research borrows from a blood test used to diagnose RA, which detects anti-citrullinated protein antibodies in the blood. While it had previously been established that such antibodies are present in patients with RA as a result of the autoimmunity response of early-stage RA to the presence of citrullinated proteins (CPs) in their blood, this was not believed to be the case with OA.

However, despite the lack of anti-CP antibodies in OA patients, researchers at the University of Warwick's Medical School found increased CP levels in both early-stage RA and OA patients. Through the creation of an algorithm of three biomarkers – CPs, anti-CP antibodies and hydroxyproline, a bone-derived amino acid that is the major component of collagen – the researchers found they could potentially detect and discriminate between OA and RA at the early stages, even before damage to the joints has occurred.

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

"Detection of early stage-OA made the study very promising and we would have been satisfied with this only," added Dr Rabbani. "But beyond this we also found we could detect and discriminate early-stage RA and other inflammatory joint diseases at the same. 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."

The team's research appears in the journal Nature Scientific Reports.