Test guide
Complement Blood Test
A complement blood test measures the levels and/or activity of a group of proteins that are part of the complement system. This system "complements" or enhances your body's defenses against infections and other diseases. Your immune system makes antibodies, which are proteins to fight disease-causing substances like viruses and bacteria. The proteins in the complement system will also help fight the infection or disease. These proteins work together in a sequence, with one protein activating the next.
What it is for
A complement blood test is most often used to diagnose or monitor autoimmune diseases such as: It may also be used to help diagnose certain bacterial , viral , or fungal infections. Source: MedlinePlus, National Library of Medicine. Medical test information is public domain. Source identity and definition checked automatically on 2026-10-18. No individual clinical interpretation or human reviewer is asserted.
Limitations
Reference intervals and interpretation depend on the laboratory, specimen, method and clinical context. This source definition is educational information; it does not establish a diagnosis, product approval or suitability for an individual.
Also known as
- complement antigen, compliment activity C3, C4, CH50, CH100, C1 C1q, C2, total complement test
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