C-Peptide levels: what's normal, high and low
A byproduct of insulin production. Reflects how much insulin your pancreas is making, not how much you've injected.
Medically reviewed by Youmna DiStefano, MD · Last reviewed September 2026
The short answer
C-Peptide is measured with a standard blood draw after an 8–12 hour fast. A typical reference range is 1.10 – 4.40 ng/mL. At TestWell it's $29.99 all-in as C-Peptide, results in 2–4 business days, drawn at Labcorp. An out-of-range result is a prompt to look closer, not a diagnosis.
- Units
- ng/mL
- Sample
- Blood draw
- Fasting
- 8–12 hours
- Results
- 2–4 business days
- Price
- $29.99
- Labs
- Labcorp · BioReference in NY/NJ
C-Peptide Reference Range
These are the typical adult reference ranges used by major US labs. Your report will include the specific range used by the lab that processed your sample.
| Population | Range |
|---|---|
| age 18+ | 1.10 – 4.40 ng/mL |
Reference ranges are educational. Always interpret your result with the specific range printed on your lab report and discuss anything outside the range with a clinician.
Have a result in hand? analyze it with your AI assistant using these reviewed ranges, or run it through our explainer. Tools: look up another marker's range · convert lab units
What does a high C-Peptide mean?
C-peptide is released with insulin, so a high level means the pancreas is making a lot of insulin — insulin resistance and early type 2 diabetes, obesity, PCOS, some medications, or reduced clearance in kidney disease. Very high values with low glucose raise the question of an insulinoma or sulfonylurea use. Unlike insulin assays, C-peptide is unaffected by injected insulin.
Common causes of a high C-Peptide
- Insulin resistance, prediabetes, early type 2 diabetes
- Obesity, PCOS, metabolic syndrome
- Sulfonylurea or meglitinide medication
- Chronic kidney disease (slower clearance)
- Insulinoma (rare; with hypoglycemia)
Ordered from most to least common.
Symptoms that can go with it
- Often none
- Weight gain around the middle, hunger, afternoon crashes
- Sweating, shakiness, confusion if glucose is low
What clinicians usually check next
- Fasting glucose and A1c drawn at the same time
- Kidney function
- If glucose is low: supervised fasting evaluation for insulinoma
Follow-up tests at TestWell: Glucose ($14.99).
Why test C-peptide instead of insulin?
It lasts longer in the blood, is not confused by injected insulin, and reflects the pancreas's own output — useful for telling type 1 from type 2 and for insulinoma work-ups.
Educational only — not a diagnosis. A single result outside the range is a prompt to look closer with a clinician.
What does a low C-Peptide mean?
Low C-peptide means the pancreas is producing little insulin. With high glucose it indicates insulin deficiency — type 1 diabetes, late-stage type 2, pancreatitis or pancreatectomy — and helps decide whether insulin therapy is needed. With normal glucose after a long fast it can simply reflect appropriate suppression. Samples must be handled promptly; delays lower it.
Common causes of a low C-Peptide
- Type 1 diabetes (including LADA in adults)
- Long-standing type 2 diabetes with beta-cell exhaustion
- Chronic pancreatitis, pancreatic surgery, cystic fibrosis
- Prolonged fasting (appropriately low)
- Delayed sample processing
Ordered from most to least common.
Symptoms that can go with it
- Thirst, urination, weight loss, fatigue when glucose is high
- None when glucose is normal
What clinicians usually check next
- Glucose and A1c at the same draw
- GAD-65 and other islet antibodies if type 1/LADA is possible
- Endocrinology review for insulin decisions
Follow-up tests at TestWell: Glucose ($14.99).
Can C-peptide tell type 1 from type 2 diabetes?
Largely yes. Low C-peptide with high glucose suggests type 1 or insulin-deficient diabetes; normal or high C-peptide suggests type 2. Antibodies complete the picture.
Educational only — not a diagnosis. A single result outside the range is a prompt to look closer with a clinician.
How do you get a C-Peptide test?
Order online, a licensed physician reviews the requisition, and you walk into a nearby lab for the draw. C-Peptide is available on its own or inside these panels — panels cost less per marker when you want the fuller picture.
| Option | Includes | Price |
|---|---|---|
| C-Peptide | This marker only | $29.99 |
| Pre-Diabetes Panel | 5 tests | $89.99 |
| Total Body Essentials Panel | 39 tests | $399.99 |
| Total Body Panel | 49 tests | $599.99 |
| Men's Total Body Advanced Panel | 65 tests | $999.99 |
Quest vs. Labcorp for C-Peptide: which lab should you pick?
Both are CLIA-certified national labs and the result is clinically equivalent, so pick whichever location is closer. Your report will print that lab's own reference range, which can differ slightly from the table above.
| Lab | Available | Price |
|---|---|---|
| Quest Diagnostics | No | — |
| Labcorp | Yes | $29.99 |
| BioReference (NY & NJ) | Yes | $39.99 |
Need help choosing a location? Use the lab finder to see draw sites near your ZIP.
Related Diabetes & Blood Sugar biomarkers
Markers commonly tested alongside C-Peptide.
Frequently asked
What does a high C-Peptide mean?
C-peptide is released with insulin, so a high level means the pancreas is making a lot of insulin — insulin resistance and early type 2 diabetes, obesity, PCOS, some medications, or reduced clearance in kidney disease. Very high values with low glucose raise the question of an insulinoma or sulfonylurea use. Unlike insulin assays, C-peptide is unaffected by injected insulin.
Why test C-peptide instead of insulin?
It lasts longer in the blood, is not confused by injected insulin, and reflects the pancreas's own output — useful for telling type 1 from type 2 and for insulinoma work-ups.
What does a low C-Peptide mean?
Low C-peptide means the pancreas is producing little insulin. With high glucose it indicates insulin deficiency — type 1 diabetes, late-stage type 2, pancreatitis or pancreatectomy — and helps decide whether insulin therapy is needed. With normal glucose after a long fast it can simply reflect appropriate suppression. Samples must be handled promptly; delays lower it.
Can C-peptide tell type 1 from type 2 diabetes?
Largely yes. Low C-peptide with high glucose suggests type 1 or insulin-deficient diabetes; normal or high C-peptide suggests type 2. Antibodies complete the picture.
Do I need a doctor's order to test my c-peptide?
No. TestWell's licensed physician network reviews and approves your order — usually within minutes. You can place an order online without an in-person visit or a referral from your own doctor.
How long does it take to get C-Peptide results?
Most C-Peptide results are available in 1–3 business days after your specimen arrives at the lab. You'll get an email the moment your results are ready, with everything viewable in your TestWell portal.
How much does a C-Peptide test cost?
Our C-Peptide starts at $29.99. That's the all-in price — no copays, no insurance hoops, no surprise bills. HSA and FSA cards are accepted.
Do I need to fast before my C-Peptide test?
Yes — for the most accurate result, fast for 8–12 hours before your blood draw. Water is fine; coffee, food, and supplements are not. Your prep instructions will be included with your order.
Which lab will process my C-Peptide test?
Your test will be processed by Quest Diagnostics, Labcorp, or BioReference depending on which is closest to you and which lab carries the test. All three are CLIA-certified and trusted by hospitals nationwide. You'll choose your lab during checkout from 4,000+ locations.
Ready to test your c-peptide?
Order in two minutes, get physician-approved, and visit a lab the same day. Starts at $29.99.