All tests
Blood tests
Complement (C3 and C4)
Proteins of the immune system that get used up during some types of inflammation.
Video lesson
Why it’s ordered
To monitor lupus activity, especially kidney disease.
Understanding results
Low C3 and C4 often signal active lupus. Rising levels after treatment suggest the disease is settling.
Good to know
Some people inherit low C4 without it meaning active disease.
At a glance
Type
Blood tests
Reviewed by Farhan Tahir, MD, FACR
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Book an in-person or telehealth consultation with Dr. Tahir.
For education only. Don’t start, stop or change a medicine without talking to your care team.