To evaluate ferritin concentration in serum and synovial fluid (SF) as a marker of activity of arthritis in comparison with C-reactive protein (CRP) and acute-phase serum amyloid A protein (A-SAA).
We determined the concentrations of ferritin, CRP and A-SAA in paired serum and SF in 34 rheumatoid arthritis (RA) and 21 osteoarthritis (OA) patients. The erythrocyte sedimentation rate (ESR) was also measured.
The serum concentrations of ferritin, CRP and A-SAA were 93 +/- 76 (mean +/- SD) ng/ml, 4 +/- 5 mg/ml, 8 +/- 4 mg/ml in OA and 140 +/- 227, 59 +/- 34, 289 +/- 223 in RA, respectively. There was no significant difference in serum ferritin levels between OA and RA, and serum ferritin did not correlate with ESR, CRP or A-SAA. Both serum CRP and A-SAA levels were significantly higher in RA than in OA (p < 0.0001, p < 0.0001), and correlated with ESR in all arthritis (r = 0.658, p < 0.0001, r = 0.404, p < 0.01), respectively. Serum CRP levels correlated with A-SAA levels in serum (r = 0.727, p < 0.0001). In SF, the concentrations of ferritin, CRP and A-SAA in RA (421 +/- 307, 25 +/- 20 and 39 +/- 41) were significantly higher (p < 0.01, p < 0.0001, p < 0.001) than those in OA (202 +/- 220, 2 +/- 2 and 2 +/- 2), respectively. There were significant correlations among SF ferritin, CRP and A-SAA.
Ferritin levels in SF but not in serum are significantly elevated in RA more than in OA, and ferritin correlated with CRP or A-SAA in SF, but not in serum. Higher levels of SF ferritin, as well as SF CRP and SF A-SAA, seem to reflect greater degrees of joints inflammation in RA and OA.