C‐Reactive Protein in Systemic Lupus Erythematosus

The presence of C‐reactive protein (CRP) was determined in the sera of 70 patients with systemic lupus erythematosus (SLE), 24 patients with rheumatoid arthritis (RA), and 17 patients hospitalized with acute infections. CRP (precipitin reaction > 3 mm) was present in only 2 of 50 patients with active, uncomplicated SLE (4%). However CRP was found in the sera of 11 patients with active SLE in the presence of superimposed infection. Treatment of the intercurrent infection resulted in the loss of CRP from the sera of these SLE patients. CRP was found in 85% of patients with active RA and in 100% of non‐SLE infected patients. Appropriate treatment of the latter group resulted in loss of CRP from the convalescent sera. Corticosteroid therapy did not appear to influence the presence of CRP in the RA or SLE groups. Fourteen of 50 noninfected patients (28%) with active SLE were not receiving steroids at the time of CRP negativity. Appropriate experiments with mixed sera failed to demonstrate serum factors that could influence CRP precipitation in the CRP‐negative SLE group. These studies suggest that patients with active SLE usually do not have CRP in their sera, and the results distinguish this group of patients from those with active RA, a disease generally marked by CRP positivity. Moreover, the finding of significant CRP precipitin in the sera of SLE patients may suggest the presence of superimposed infection.