C-reactive protein and serological indices of disease activity in systemic lupus erythematosus.

The concentration of C-reactive protein (CRP) in sera from 70 patients with systemic lupus erythematosus (SLE) showed no correlation with commonly accepted laboratory indices of disease activity. Most patients had detectable serum CRP, but in some patients CRP was not found despite repeated testing. This absence of a CRP response did not appear to be related to medication. In some patients high levels of CRP were seen in the absence of infection. Measurement of serum CRP in SLE is unlikely to be useful in the laboratory diagnosis of disease activity.