Synovial fluid ferritin in rheumatic diseases

The synovial fluid ferritin level in 49 patients (57 joints) with various rheumatic diseases was analysed. In rheumatoid arthritis (n = 22) the geometric mean ferritin level was 528 micrograms/l (range 56-3 100 micrograms/l), in other inflammatory arthritides (n = 12) 339 micrograms/l (105-2 835 micrograms/l) (p greater than 0.5), in calcium pyrophosphate arthropathy (n = 14) 507 micrograms/l (180-4 230 micrograms/l) (p greater than 0.5) and in non-inflammatory osteoarthritis (n = 9) 167 micrograms/l (14-725 micrograms/l) (p less than 0.05). Synovial fluid/serum ferritin ratios did not differ significantly in the four diagnostic groups; 4 patients had ratios less than 1.0. Synovial fluid ferritin was not correlated to total fluid cell count or differential cell count. Although ferritin content was significantly greater in inflammatory than in noninflammatory fluid (p less than 0.05), the wide scatter of the values and marked overlap between the different groups limit the value of measuring synovial fluid ferritin as a differential diagnostic test for rheumatic diseases.