Interpret Your Complement C3 Results
Enter your C3 value below and get an instant, free AI interpretation — a plain-English explanation checked against WHO/IFCC reference ranges.
Medical Disclaimer
This AI-generated interpretation is for educational purposes only and does not constitute medical advice, diagnosis, or treatment. Results may vary based on individual health factors not captured here.
Always consult a qualified healthcare professional before making any health decisions. Read full disclaimer →
Complement C3 Normal Ranges
C3 (Complement component 3) is the most abundant protein in the complement system — the arm of innate immunity responsible for clearing pathogens and immune complexes.
| Age Group | Reference Range | Unit | Notes |
|---|---|---|---|
| Adults (18–64) | 90 – 180 | mg/dL | — |
Also reported in: g/L.
Why Doctors Order the Complement C3 Test
Low C3 combined with low C4 is the classic laboratory pattern of active Systemic Lupus Erythematosus (SLE), particularly lupus nephritis. In lupus, immune complexes (containing anti-dsDNA) deposit in tissues and activate complement, consuming both C3 and C4.
How to Enter Your C3 Result
Complement C3 can be reported in mg/dL or g/L. Choose the unit printed next to your result on the lab report so it is compared with the matching reference range.
What a Low or High C3 Can Be Associated With
Below the reference range
- Active SLE / lupus nephritis (immune complex consumption — most common clinical cause)
- Membranoproliferative glomerulonephritis (MPGN) with C3 nephritic factor
- Post-streptococcal glomerulonephritis (transient, normalizes within weeks)
- Hereditary C3 deficiency (rare — presents with severe recurrent bacterial infections)
- Cryoglobulinemia
Above the reference range
- Acute phase reaction (infection, trauma, malignancy — C3 is an acute phase protein)
- Obesity
- Pregnancy
These are common associations, not a diagnosis. A single result is read alongside your symptoms, history and other tests — discuss it with your doctor.
What Can Change Your C3 Result
Before you read too much into a result, consider whether any of these applied:
- Sample handling (C3 degrades if sample sits at room temperature — process promptly or keep on ice)
- Acute phase reaction can mask low C3 (infection or inflammation raises C3, hiding lupus-related consumption)
- Rare C3 null alleles can cause constitutional low C3 without disease
Preparing for the test: No fasting required. C3 should be measured alongside C4 and anti-dsDNA for complete lupus activity assessment.
Symptoms That Often Prompt C3 Testing
- In lupus: butterfly rash, joint pain, fatigue, kidney involvement (foamy urine)
- In complement deficiency: recurrent bacterial infections (encapsulated bacteria)
- In glomerulonephritis: blood in urine, frothy urine, elevated creatinine, hypertension
Want the full clinical guide to Complement C3?
Reference ranges, causes, symptoms, preparation, and FAQs.