Future Blood Test for Osteoarthritis Uses Current Assays

Ahmed U, Anwar A, Savage RS, et al., Biomarkers of early stage osteoarthritis, rheumatoid arthritis and musculoskeletal Health.Nature Scientific Reports. 2015;5:9259. doi: 10.1038/srep09259.

Elevated citrullinated proteins (CPs), a biomarker linked to early rheumatoid arthritis (RA), are also found in patients with early-stage osteoarthritis (OA) – and could be used in a blood test to detect OA years before radiographic damage appears, say these authors.

Research at the University of Warwick UK finds high levels of CPs in patients with early OA and early RA, but autoimmune-linked anti–CCP antibodies (anti-CCPs) occur mostly in early RA. Anti-CCPs are not present in even advanced OA.

Combined in a single assay, three biomarkers-CPs, anti-CCPs, and the bone-derived substance hydroxyproline (Hyp)-could help distinguish between OA and RA early enough to prevent joint damage, the researchers say.

The combined experimental algorithm using this assay has high specificity in both early OA and early RA (87% and 91%, respectively) and shows good sensitivity in OA (73%), compared with healthy controls and patients without RA.

"It has been long established that the autoimmunity of early-stage RA leads to antibodies to CPs, but the autoimmunity, and hence antibodies, are absent in early-stage OA,” explains lead researcher Naila Rabbani PhD, an Associate Professor of Experimental Systems Biology at Warwick’s Medical School.

“Using this knowledge and applying the algorithm of biomarkers we developed provides the basis to discriminate between these two major types of arthritis at an early stage,” she said in a press release.

Limitations of the current study include the small number of patients (n=181) and the experimental nature of the assay, the authors note. The findings need validation in larger numbers of patients and the biochemical validity assay needs independent confirmation as well.

Testing for anti-CCPs and rheumatoid factor (RF) is routinely done in diagnosing RA. Anti-CCP is also included in a current panel of assays that can help distinguish OA from RA. That panel (IdentRA™) combines tests for anti-CCP, rheumatoid factor (RF), and a novel biomarker, 14-3-3-ŋ (eta).

The protein 14-3-3-ŋ is elevated in RA, psoriatic arthritis (PsA), and other rheumatic diseases. but not in OA.