Complement Blood Test
Reviewed
Measures the levels and/or activity of complement proteins (C1–C9, often C3, C4, or CH50/CH100) to help diagnose or monitor autoimmune diseases like lupus and rheumatoid arthritis, and to help diagnose certain infections.
Preparation and collection
No special preparation is needed.
Understanding this test
Use the reference interval and units printed by the laboratory that performed the test. A result outside that interval is not a diagnosis by itself, and a result inside it does not rule out every condition. Your symptoms, history, medicines, timing, and related tests can change what the result means.
- Results are not diagnostic by themselves; your provider will consider your symptoms, medical history, and other tests.
- The test does not specify which condition you have; further testing may be needed.
What to do next
If you have questions about your results, talk to your provider. They will consider your symptoms, medical history, and the results of other blood tests to determine if additional tests are needed.