Copper--an index of erosive activity?

Using atomic absorption spectrophotometry the copper content of synovial fluid has been compared in rheumatoid and osteoarthrotic synovial fluids. Synovial fluid caeruloplasmin has been determined by single radial immunodiffusion. Both are significantly increased in the rheumatoid group. Serum copper, similarly estimated, shows a trend to greater elevation with increasing degree of rheumatoid erosion as assessed radiologically.