C-peptide blood test
Connecting peptide
In short
A typical adult C-peptide result is 0.8 to 3.1 ng/mL (fasting). A high C-peptide most often means the pancreas is making extra insulin to keep sugar in range. Weaker kidneys can also let it build up. Always read your result against the range printed on your own report.
A marker of how much insulin your own pancreas makes.
When your pancreas makes insulin, it releases C-peptide in equal amounts. Unlike an insulin test, it is not affected by insulin treatment, so it shows your body's own output. Doctors use it to understand diabetes type or the cause of low blood sugar.
Is my C-peptide high or low?
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Typical range
| For | Range | Unit |
|---|---|---|
| Adults · fasting | 0.8–3.1 | ng/mL |
| Adults · fasting | 265–1026 | pmol/L |
Typical ranges for adults. Labs differ a little, so the range printed next to your result is the one to go by.
If your C-peptide is high
A high C-peptide most often means the pancreas is making extra insulin to keep sugar in range. Weaker kidneys can also let it build up.
Common reasons
- Eating before the test
- Insulin resistance, when the body responds less to insulin, often with weight gain
- Kidneys that clear less C-peptide
- Steroid medicines, or diabetes medicines that push the pancreas to release insulin
- Less often: a rare tumor that makes too much insulin
If your C-peptide is low
A low C-peptide can mean the pancreas is making little insulin. Doctors read it with glucose drawn at the same time.
Common reasons
- Low sugar at the time of the test, when little insulin is needed
- Long-standing type 2 diabetes, as insulin-making cells wear out over time
- Less often: type 1 diabetes, where the pancreas makes little or no insulin
- Less often: pancreas damage or surgery
- Less often: severe infection, liver disease or a hormone-gland problem
What can throw it off
Eating before the test raises C-peptide, and weaker kidneys can make it read higher.
Questions to take to your appointment
- 1What does this show about my own insulin production?
- 2Was my glucose checked at the same time?
- 3Could my kidneys be affecting this result?
Read together with
Doctors rarely read C-peptide alone. These usually sit next to it.
Quick answers
What is the C-peptide blood test?
C-peptide (Connecting peptide): A marker of how much insulin your own pancreas makes. When your pancreas makes insulin, it releases C-peptide in equal amounts. Unlike an insulin test, it is not affected by insulin treatment, so it shows your body's own output. Doctors use it to understand diabetes type or the cause of low blood sugar.
What is a normal C-peptide level?
For most adults, C-peptide is typically 0.8 to 3.1 ng/mL (fasting). Some countries print it in pmol/L, so check the unit first. Labs differ a little, so the range printed next to your result is the one to go by.
What does a high C-peptide mean?
A high C-peptide most often means the pancreas is making extra insulin to keep sugar in range. Weaker kidneys can also let it build up. Common reasons include eating before the test; insulin resistance, when the body responds less to insulin, often with weight gain; kidneys that clear less C-peptide; and steroid medicines, or diabetes medicines that push the pancreas to release insulin. A doctor reads it together with your other results and how you feel.
What does a low C-peptide mean?
A low C-peptide can mean the pancreas is making little insulin. Doctors read it with glucose drawn at the same time. Common reasons include low sugar at the time of the test, when little insulin is needed; long-standing type 2 diabetes, as insulin-making cells wear out over time; less often: type 1 diabetes, where the pancreas makes little or no insulin; and less often: pancreas damage or surgery.
What can affect my C-peptide result?
Eating before the test raises C-peptide, and weaker kidneys can make it read higher.
What should I ask my doctor about my C-peptide?
Questions worth taking to the appointment: What does this show about my own insulin production? Was my glucose checked at the same time? Could my kidneys be affecting this result?
What this page can’t do
It reads each number on its own.
Doctors read results together — ALT with AST, ferritin with hemoglobin, TSH with free T4. A pattern says more than any single flag.
It doesn't know you.
Your age, your medicines, how you feel and your last result all change what a number means.
It doesn't remember.
Close this page and your results are gone. That's on purpose: nothing was ever sent to us.
We also make Vita: Health Coach, an app for those parts. It reads your whole report with your medicines and history in mind, answers follow-up questions in plain words, and keeps your reports in one place — for you and for the people you look after.
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