C-Peptide, Blood Test
This page explains the c-peptide, blood test, what it measures, and how to arrange it. A C-peptide blood test measures a substance your pancreas releases when it makes insulin. Because C-peptide and insulin are released together, this test helps show how much insulin your body is producing. It is often ordered when a doctor is evaluating low blood sugar, distinguishing types of diabetes, or checking how well the pancreas is working.
- Sample type
- blood
- Category
- Metabolic & Glucose
- Turnaround
- 1-3 business days
- Price
- $198
- Referral
- Not required
A C-peptide blood test measures a substance your pancreas releases when it makes insulin. Because C-peptide and insulin are released together, this test helps show how much insulin your body is producing. It is often ordered when a doctor is evaluating low blood sugar, distinguishing types of diabetes, or checking how well the pancreas is working.
What it measures
- C-peptide — The main marker; reflects how much insulin your pancreas is releasing.
- Glucose — Often measured at the same time to compare blood sugar with insulin production.
- Insulin — Sometimes checked alongside C-peptide for a fuller picture of insulin activity.
- Hemoglobin A1c — A longer-term average of blood sugar, sometimes added for context.
Who it is for
A doctor may order this test if you have symptoms of low blood sugar, have diabetes that is hard to classify, or are being checked for a pancreas or insulin-related condition. It is not a routine screening test for most people.
Preparation
Your doctor may ask you to fast for 8 to 12 hours before the test, depending on what else is being measured. If no fasting is needed, you can eat and drink normally. Follow the specific instructions you are given.
Results and what they mean
Results are reported as a C-peptide level, usually in nanograms per milliliter, along with any other markers measured. Your clinician interprets the number together with your symptoms, glucose level, and medical history. This is general information only and is not medical advice; discuss your results with a qualified clinician.
How to order this test
- Choose the test and place a confidential order online.
- Select a certified collection site and pick a time that suits you.
- Have your specimen collected — most draws take only a few minutes.
- Review results in a secure portal, typically within 1–3 days.
Preparation, hours, and pricing vary by site; confirm details directly with the lab before your visit.
Availability by state
Direct-access online ordering for the c-peptide, blood test is available in most states. It is currently unavailable in 6 states:
Everywhere else you can order confidentially and collect your sample at a certified site. Browse by state →
Frequently asked questions
Do I need to fast for a C-peptide test?
Sometimes. Fasting is often requested, but it depends on your doctor's instructions and whether other tests are being done at the same time.
Does this test diagnose diabetes?
It is not used alone to diagnose diabetes. It helps show how much insulin your pancreas is making, which can support a diagnosis your clinician is already evaluating.
Can I take my usual medications?
Ask your doctor first. Some medicines can affect insulin and C-peptide levels, so your clinician may adjust timing or give specific guidance.
How long until results are ready?
Typical turnaround is about 1 to 3 business days, though this can vary by laboratory.