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C3 complement component in blood
Last reviewed: 06.07.2025
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Reference values (norm) for C3 content in blood serum are 0.55-1.2 g/l.
C3 is a key component of complement, necessary for the implementation of cytolysis. It is synthesized in the liver and is part of the formed immune complexes. C3 is activated by the classical pathway by complexes of antigens with IgG, IgM, by the alternative pathway - by complexes of Ag with IgA, IgE, Fab-fragments of Ig, polysaccharide antigens of bacteria.
A decrease in the concentration of the C3 component in the blood serum leads to a weakening of the opsonizing function of the blood, phagocytosis, cytolysis and may be associated with a violation of its synthesis or increased catabolism, as well as its adsorption on immune complexes in autoimmune (immune complex) diseases. An increase in the concentration of C3 in the blood serum is characteristic of the acute period of infection (the "acute phase" protein). During the recovery period, the concentration of C3 is normalized.
Changes in C3 concentration in various diseases
Increased concentration
- Acute bacterial, fungal, parasitic and viral infections
- Cholestasis
- Gallstone disease
Decreased concentration
- Congenital complement defects, complement deficiency
- Autoimmune diseases
- Systemic lupus erythematosus
- Glomerulonephritis
- Recurrent infections
- Raynaud's disease
- Lymphogranulomatosis, chronic lymphocytic leukemia
- Dermatitis herpetiformis
- Immune complex diseases
- Hepatitis, liver cirrhosis
- Treatment with cytostatics and immunosuppressants
- Ionizing radiation
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