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Titer of complement activity in serum
Medical expert of the article
Last reviewed: 04.07.2025
Normally, the titer of complement activity in the blood serum of adults is 50-140 U/ml.
The serum complement titer evaluates the activity of terminal complement components during its activation via the classical and alternative pathways.
Any inflammatory process with an adequate immune response is accompanied by an increase in the complement titer. A decrease in the titer indicates a deficiency of complement and leads to a weakening of its opsonizing function and complement-dependent cytotoxicity, which contributes to the accumulation of immune complexes and leads to the chronicity of the inflammatory process. An increase in complement activity is characteristic of allergic and autoimmune processes. In severe anaphylactic reactions, the complement titer decreases, and in anaphylactic shock it may not be determined at all.
Changes in complement titer in blood serum in various diseases
Increase in the indicator
- Autoimmune diseases:
- rheumatoid arthritis;
- systemic lupus erythematosus;
- polyarteritis nodosa;
- bacterial endocarditis;
- non-specific infectious polyarthritis
- Acute bacterial infections
Decrease in the indicator
- Condition after major surgeries, purulent inflammatory processes, sepsis, peritonitis, hepatitis, liver cirrhosis, immune complex diseases
- Chronic, latent bacterial infections
- Malignant neoplasms with metastases
- Multiple myeloma
- Treatment with cytostatics and immunosuppressants