C-reactive protein in sera from patients with systemic lupus erythematosus.

One hundred and ninety sera from 27 patients with systemic lupus erythematosus (SLE) were tested by radial immunodiffusion for C-reactive protein (CRP). One hundred and fourteen (60%) of these samples from 22 patients had detectable CRP. There was a statistically significant association between clinical activity and serum concentration of CRP in the patients who consistently recorded elevated levels. CRP was not found to distinguish between disease activity and coincident infection in 2 patients whose SLE was complicated by tuberculosis.