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

Abstract

Objective: 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). Methods: 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. Results: The serum concentrations of ferritin, CRP and A-SAA were 93 ± 76 (mean ± SO) ng/ml, 4± g/ml, 8± g/mlin OA and 140±227, 59 ± 34, 289 ± 223 in RA, respectively. There was no significant differenee 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 inRA (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. Conclusion: 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.

Key Words:

• rheumatoid arthritis
• osteoarthritis
• synovial fluid
• serum amyloid A
• C-reactive protein
• Ferritin