For the first time, a biomarker-based test can diagnose early osteoarthritis (OA) and distinguish it from other types of arthritis with a high level of accuracy.
The algorithm-based tool could be particularly useful in differentiating OA from inflammatory arthritis and catching the condition earlier before cartilage has severely degraded.
This could help with the development of effective treatment plans and ensure the evaluation of alternative or additional diagnoses, particularly in cases where the clinical presentation may not be straightforward.
“This study addresses an unmet need for objective diagnosis of OA to improve clinical decision-making and patient outcomes,” said corresponding author Daniel Keter, a research senior scientist at CD Diagnostics, a division of U.S. medtech company Zimmer Biomet.
The two-step test, outlined in the Journal of Orthopaedic Research, uses levels of Cartilage Oligomeric Matrix Protein (COMP) and interleukin-8 (IL-8) in the synovial fluid of joints, which are run through an algorithm.
COMP is elevated in the synovial fluid of the affected joint when OA is present and cartilage is degraded. However, other forms of arthritis also direct cartilage breakdown and release of COMP, making an additional biomarker also necessary.
This is where IL-8 comes in. It shows low levels in OA but elevated concentrations in different forms of inflammatory arthritis, including rheumatoid arthritis, crystal arthritis, and native septic arthritis, or acute trauma.
The researchers note that primary OA is unlikely when either COMP levels or COMP/IL-8 ratio in the synovial fluid is low as these conditions indicate either lack of cartilage degradation or high inflammation.
In contrast, high COMP combined with a high COMP/IL-8 ratio would indicate low inflammation in the setting of cartilage deterioration, indicative of primary OA.
In a retrospective study, the team assessed the value of a two-step test algorithm that combined the synovial fluid COMP and IL-8 biomarkers in distinguishing OA from inflammatory arthritis in 171 human knee synovial fluid specimens.
The result was indicative of primary OA when concentrations of COMP and its ratio with IL-8 met particular thresholds.
The study included 54 samples of primary OA, 57 of rheumatoid arthritis, 30 crystal arthritis and 30 native septic arthritis. The OA algorithm, which is a component of the Synovasure RISC panel, was designed to be indicative of primary OA when COMP concentration and the COMP/IL-8 ratio met the established decision thresholds.
Based on the characteristics of native knee samples received for clinical testing, the anticipated prevalence of OA in the population was estimated to be 60%.
When the data was adjusted for 60% disease prevalence, the accuracy of the OA algorithm was 87.8%, with positive and negative predictive values of 92.2% and 82.1%, respectively.
“Looking forward, differentiating primary OA from other inflammatory arthritis types contributes towards better diagnosis that enables accurate, and targeted treatment of primary OA,” the researchers reported.
“When coupled with other synovial fluid biomarker test results, this diagnostic algorithm also objectively reveals the relative inflammatory status of the joint based on the presence of inflammatory arthroses.”
