Serum copper: a marker of disease activity in rheumatoid arthritis.

Serum copper concentrations were measured in patients with rheumatoid arthritis (RA), ankylosing spondylitis (AS), osteoarthritis (OA), and in healthy controls. Median serum copper concentrations were raised significantly in RA and AS, but not in OA. Serum copper in RA correlated significantly with a number of disease activity markers--for example erythrocyte sedimentation rate (ESR), C-reactive protein, haemoglobin concentration, morning stiffness, and grip strength. It also correlated well with the overall disease activity as assessed by a composite index. Raised serum copper was associated with severe RA as manifested by the presence of immunoglobulin M rheumatoid factor, extra-articular features, weak grip and highly active disease. High serum copper might be related to the development of the pathological lesions observed in RA and not just be a secondary response.