Complement C4
A classical-pathway complement protein that drops when immune complexes are driving disease activity.
Consider this test if:
- Known or suspected lupus, and monitoring disease activity over time
- Recurrent episodes of angioedema without hives, raising the question of hereditary angioedema
- Working up unexplained glomerulonephritis, vasculitis, or serum sickness
- Recurrent pyogenic bacterial infections suggesting a possible inherited complement deficiency
- Tracking complement levels alongside C3 during a known immune-complex condition
- HSA/FSA eligible
- Typical results in 1-2 days · Reviewed by a real clinician
- Drawn at a CLIA/CAP-accredited lab near you ·
Pre-test considerations
No fasting required. A standard blood draw, typically serum. Very high blood lipids (lipemia) and elevated rheumatoid factor can falsely increase the measured C4, so results are interpreted with that in mind.
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What this test is for
Complement C4 is a protein of the classical complement pathway, part of the immune system that helps clear pathogens and immune complexes. Low C4 reflects either consumption when the classical pathway is activated or, less commonly, an inherited deficiency, and it is a sensitive indicator of lupus (SLE) disease activity. It also drops in serum sickness, certain glomerulonephritides, chronic active hepatitis, and hereditary angioedema, where lack of C1 esterase inhibitor lets C4 be broken down unopposed. Because C4 is used only by the classical pathway, it stays normal in conditions that activate the alternate pathway alone, which is why it is usually read alongside C3 and total hemolytic activity (CH50). Lipemia and high rheumatoid factor can falsely raise the apparent C4 level.
This test measures C4 on its own. The separate C3c and C4c panel reports both proteins together, which is the more common pairing when tracking complement consumption in immune-complex disease.
What to expect
- 1 Book instantly
Click, book, done. Choose a convenient lab location near you. Transparent, up-front pricing.
- 2 Quick lab visit
Testing to fit your busy schedule, usually 15 minutes or less. Walk-in and appointments available.
- 3 Typical results in 1-2 days
Your results post straight to your dashboard as soon as the lab completes them.
- 4 Expert guidance
Included with Mito membership. A clinician reviews your results and your personalized action plan follows, with clear next steps.
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Members pay our cost on every test, with lab fees passed straight through. The full receipt is itemized, never padded.
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Order any test or consult without joining. For $9/month, members unlock member prices, trend tracking, and year-round clinician guidance.
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Frequently asked questions
View all FAQsHow does pricing work?
Every test shows the member price next to the standard non-member price, so you can see what membership saves you. The member price is our cost — covering the lab and what it takes to run the service — never a profit on the test itself; Mito makes its money on the $9 membership, not on marking up your tests. Membership is $9/mo, and you still pay the lab’s order fee. Prices are itemized before you pay, with no hidden fees.
Where do I get tested?
Choose a partner lab (Quest, Labcorp, or BioReference) at checkout. If your cart spans multiple tests, we consolidate the whole order onto a single lab so you only make one visit.
Is this eligible for HSA/FSA?
Yes. This test is HSA/FSA eligible, and you can pay with your HSA/FSA card at checkout.
When will I get my results?
Your results post to your dashboard once your lab completes them, then a clinician reviews them and your full analysis and personalized action plan (with clear next steps) follow. Turnaround varies by test: specialty assays and at-home kits take longer, and each test shows its expected turnaround before you buy.
Do I need a doctor’s order?
No. Mito provides the lab order for you, so you can book and get tested without a separate doctor visit.
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