Serum amyloid-A protein concentration in rheumatoid arthritis and its role in monitoring disease activity.

The serum concentrations of serum amyloid-A protein (SAA), C-reactive protein (CRP), and alpha 1-acid glycoprotein (alpha 1-AGP) have been measured in 185 patients with rheumatoid arthritis. SAA and CRP concentrations correlated well (r = 0.86) both within and above the normal ranges, though SAA showed a greater incremental increase than CRP. All patients with normal SAA levels also had normal CRP and alpha 1-AGP concentrations. In contrast, in 40% of patients with normal CRP and alpha 1-AGP concentrations the SAA was raised, sometimes markedly so. The clinical and serological assessments of disease activity in these patients were not significantly different from those with concomitantly raised levels of CRP. These findings suggest that SAA is a more sensitive marker of inflammation than is CRP. The role of the measurement of SAA as a monitor for inflammatory disease activity is discussed.