C-Peptide, Serum
Released in equal amounts to insulin when the pancreas produces it — but cleared more slowly, giving a stable picture of your own insulin production.
Distinguishes insulin your body made from insulin you injected, and measures true beta-cell function. Useful for separating type 1 from type 2 diabetes and assessing pancreatic reserve.
Optimal ranges, root causes, and the complete correction protocol — nutrition, supplements, lifestyle, hormones and peptides — plus 100+ other markers.
Unlock everything — $10/mo →📚 American Diabetes Association Standards of Care — C-peptide in diabetes classification.
🩸 Test your C-Peptide, Serum
Order directly through Marek Diagnostics — no doctor's visit needed, drawn at any Quest location in the US. Code CAMERON applies 10% off automatically.
Order this test — 10% off → Browse all 102 markers →What C-Peptide, Serum is usually tested alongside
On its own, one marker is a data point. These panels include C-Peptide, Serum plus the markers that make it interpretable — each names every test, why it is on the list, and loads the whole set into your cart in one click at 10% off.
includes this + 8 more markers — Prediabetes, PCOS, stubborn central weight, a family history of diabetes, or a normal HbA1c you don't trust.
Why your C-Peptide, Serum might be wrong
Most abnormal results are interference, not disease. These are the things that measurably move this specific marker — check them before you change anything. Each one says whether the number is wrong and should be repeated, badly timed and should be redrawn, or real with a cause worth explaining.
Rises after eating, so a non-fasted draw measures your breakfast rather than your baseline.
Draw fasted, 10–12 hours, water only.
C-peptide is the point of this test: injected insulin contains none, so a low C-peptide with a high insulin means the insulin came from outside the body. That is the intended use, not an artefact.
Note any insulin use — it changes the interpretation entirely.
C-peptide is cleared by the kidney, so impaired function raises it without any change in pancreatic output.
Read against eGFR, ideally cystatin C-based.
What C-Peptide, Serum means in combination
A single marker tells you a little. Combinations tell you the story — these are the named patterns this marker takes part in, and what each one points at.
C-peptide confirms the pancreas is still producing well, so this is a receptor-side problem rather than a production one. That distinction changes what actually helps.
Everything that improves insulin sensitivity applies and is likely to work: resistance training, fat loss, sleep, fibre, post-meal walking. A genuinely low C-peptide is the opposite situation and needs a clinician promptly.
What to test next
Markers rarely answer alone. These are the ones that put C-Peptide, Serum in context — each with its own full breakdown.
Frequently asked questions
0.80–3.85 ng/mL (fasting) Ranges vary by laboratory and assay — always compare to the range printed on your own report.
Optimal ranges, root causes and the full correction protocol are available inside Coach Cam's Peptide Academy.
See the full breakdown inside the Academy.
See the full breakdown inside the Academy.
You can order C-Peptide, Serum directly through Marek Diagnostics without a doctor's visit — drawn at any Quest Diagnostics location in the US. Code CAMERON applies 10% off automatically.