Acute-phase proteins and serum immunoglobulins in ankylosing spondylitis.

The erythrocyte sedimentation rate (ESR) and the serum acute-phase proteins (APP), C-reactive protein (CRP), fibrinogen, 9th component of complement (C9), and alpha, antitrypsin were measured on 231 occasions in 80 patients with ankylosing spondylitis and compared with those in 30 controls. APP levels did not correlate with clinical assessment of disease activity. However, there were significant correlations between CRP, C9, and fibrinogen (p = less than 0.01), suggesting that these APP may be more reliable indicators of disease activity. The mean values of the APP in those patients with a peripheral arthritis were significantly higher than in those with pelvospondylitis alone for ESR (p less than 0.01), CRP (p less than 0.01), and fibrinogen (p less than 0.05). The only significant difference between those patients with an iritis and those with only pelvospondylitis was an elevated CRP in the iritis group (p less than 0.01). This suggests that a peripheral arthritis is the most important cause of an elevated ESR or APP in ankylosing spondylitis. Serum immunoglobulins were also measured and they showed a significant elevation of IgA in all 3 patients groups, there being no difference between each group. Serum IgG was raised only in those patients with an iritis or peripheral arthritis, the IgM levels being within the normal range for all patient groups.