Plasma C3d/C3 quotient as a parameter for in vivo complement activation

J Immunol Methods. 1984 Nov 16;74(1):87-91. doi: 10.1016/0022-1759(84)90370-3.


Plasma levels of C3 and C3d in 30 healthy donors and 58 patients with systemic lupus erythematosus were determined by rocket immunoelectrophoresis and Con-A affinoimmunoelectrophoresis. Significantly decreased levels of C3 were found in approximately 50% of the SLE sera. Slight increases of free C3d were found in 55%, and marked increases in 9% of the SLE sera; the remaining SLE sera did not show increased C3d levels. When results were expressed as quotients of plasma C3d/C3, a significant pattern emerged and 70% of the SLE sera clearly fell outside the normal range. 10% of the SLE sera had normal C3d/C3 indices but had markedly depressed C3 levels. We conclude that in cases where total serum C3 is not markedly reduced (less than 60% of normal), the C3d/C3 quotient may be a more sensitive parameter for assessing in vivo complement activation than C3 or C3d determinations alone.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Complement C3 / analysis*
  • Complement C3d
  • Concanavalin A
  • Enzyme Activation
  • Humans
  • Immunoelectrophoresis, Two-Dimensional / methods
  • Lupus Erythematosus, Systemic / blood
  • Reference Values


  • Complement C3
  • Concanavalin A
  • Complement C3d