Complement Component 3
Inflammation marker
Complement C3
Complement Component 3
A central protein of the complement system, part of innate immunity. Levels fall when complement is consumed by immune-complex disease (notably active lupus) and rise as a non-specific acute-phase reactant.
PED Notes
Complement C3 is not affected by AAS, GH, or peptides. It matters for enhanced athletes mostly as part of an autoimmune work-up: a low C3, especially with a low C4 and positive anti-dsDNA, points to active systemic lupus, which can masquerade as training fatigue, joint pain, or unexplained abnormal bloodwork. As an acute-phase protein, C3 can also rise modestly with inflammation, infection, or heavy training, so a high value is far less specific than a low one. The clinically important direction is LOW (consumption). The bodybuilder range equals the standard range.
When high
When elevated (>1.8 g/L):
- A high C3 is a non-specific acute-phase response to inflammation, infection, or tissue injury, including from intense training or high body fat.
- What to do: it rarely needs action in its own right. Ensure a rested blood draw and interpret alongside CRP and ESR. Persistent elevation with other inflammatory markers warrants looking for a chronic inflammatory source.
When low
When low (<0.9 g/L) -- the clinically important direction:
- A low C3 suggests complement is being consumed, classically by immune-complex disease such as active systemic lupus erythematosus, lupus nephritis, or certain types of glomerulonephritis. Rarely it reflects inherited complement deficiency or advanced liver disease (reduced synthesis).
- What to do:
- Do not dismiss a low C3; seek medical review, particularly with a low C4, positive ANA or anti-dsDNA, rash, joint pain, or kidney abnormalities.
- Falling C3 and C4 over time can signal a lupus flare, so trend them together.
- Interpret with urinalysis and kidney function, since lupus nephritis is a key concern.
History Chart
Reading History
Frequently Asked Questions
Reference Ranges
Standard Range
VitalMetrics Range