Ferritin correlates with C-reactive protein and acute phase serum amyloid A in synovial fluid, but not in serum

Objective: To evaluate ferritin concentration in serum and synovial fluid ( SF) as a marker of activity of arthritis in comparison with C-reactive prot ein (CRP) and acute-phase serum amyloid A protein (A-SAA). Methods: We dete rmined the concentrations of ferritin, CRP and A-SAA in paired serum and SF in 34 rheumatoid arthritis (RA) and 21 osteoarthritis (OA) patients. The e rythrocyte sedimentation rate (ESR) was also measured. Results: The serum c oncentrations 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 +/- 22 3 in RA, respectively. There was no significant difference in serum ferriti n 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 arthriti s (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 conc entrations 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) that those in OA (202 +/- 220, 2 +/- 2 and 2 +/- 2), respectively. There were significan t correlations among SF ferritin, CRP and A-SAA. Conclusion: Ferritin level s 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 l evels of SF ferritin, as well as SF CRP and SF A-SAA, seem to reflect great er degrees of joints inflammation in RA and OA.