C4 is decreased when classical pathway of complement is hyperactivated. It is usually decreased in hypergammaglobulinemia, cryoglobulinemia, inborn C4 deficiency, active SLE, serum sickness, SBE, chronic active hepatitis, acute glomerulonephritis and rheumatoid arthritis, as well as in hereditary angioneurotic edema.
Adult: 13-60 mg/dl
- Complement C4
- Fourth Component of Complement
- C4 COMPLEMENT
C4 comprises approximately 20% of the complement system. C4 is utilized only by the classical pathway, so that it is decreased only when this arm is hyperactivated. In diseases activating the alternate pathway alone, C4 levels will be normal. Total hemolytic activity (CH50), C3, and C4 are frequently decreased in a variety of conditions relating to immune complex formation. While many complement components are depressed with uremia, C4 is an exception and is elevated with uremia.