Serum C3 and C4 complement components in ulcerative colitis and Crohn's disease.

Serum C3 and C4 complement components were estimated in patients with Crohn's disease and ulcerative colitis. In Crohn's disease, serum C4 concentrations were significantly higher than those of controls. In ulcerative colitis, significantly higher concentrations of C3 and C4 were associated with severe or extensive disease, and C4 concentrations may remain high, years after total colectomy.