Knee arthritis could become easier to detect and diagnose thanks to a new test involving the lubricating fluid inside the joint.

A new study shows that arthritis of the knee often is diagnosed in its late stages, after cartilage has degraded and bones are rubbing against each other in the joint.

At that point, it’s tough to tell whether knee arthritis has been caused by natural wear and tear, or if an inflammatory disease is behind a person’s joint problems, the researchers noted in a new study published Dec. 18 in the Journal of Orthopaedic Research.

But a new test involving two markers found in the synovial fluid of patients’ joints might be able to help docs suss all this out more promptly.

The test “addresses an unmet need for objective diagnosis of osteoarthritis to improve clinical decision-making and patient outcomes,” researcher Daniel Keter with CD Diagnostics, a division of Zimmer Biomet, said in a journal news release.

The fluid test looks for a protein called cartilage oligomeric matrix protein (COMP), as well as an inflammatory biochemical called interleukin-8 (IL-8), researchers said.

COMP levels tend to be high in the synovial fluid of people with “wear-and-tear” osteoarthritis, because it’s released as cartilage breaks down.

On the other hand, IL-8 is low in osteoarthritis but elevated in people with inflammatory conditions like rheumatoid arthritis.

Using these two markers, researchers were able to accurately diagnose “wear-and-tear” osteoarthritis about 87% of the time in 171 knee synovial fluid specimens.

Up to 15% of U.S. adults 60 and older suffer from osteoarthritis, and it’s expected to become even more prevalent due to the aging population and the increase in risk factors like obesity, researchers noted.

A test like this could help steer people to the best arthritis treatment for them, and do so in a more timely way.

“Differentiating primary osteoarthritis from other inflammatory arthritis types contributes towards better diagnosis that enables accurate and targeted treatment of primary osteoarthritis,” the research team concluded.

However, they added that more research is needed to validate the test before it’s ready to be widely used.