C-Peptide
A blood test that measures C-peptide levels to evaluate how much insulin the pancreas produces and help distinguish between Type 1 and Type 2 diabetes.
Order this test
LevelPanel has no business or affiliate relationship with Quest or LabCorp. These links are provided as a public service.
Lab testing services linked from this site are not available to residents of Alaska, Arizona, or Hawaii, unless otherwise noted on the lab's own website.
This publication is not intended to solicit the purchase of laboratory testing from any individual consumer.
What this test measures
C-peptide is a short chain of amino acids that the pancreas produces in equal amounts alongside insulin. When blood sugar rises after eating, the pancreas assembles a precursor molecule called proinsulin, which is then split into two pieces: active insulin and C-peptide. Both are released into the bloodstream simultaneously and in a one-to-one ratio, making C-peptide a reliable proxy for how much insulin the body is manufacturing on its own.
What makes C-peptide especially useful is that it lingers in the bloodstream longer than insulin and, critically, is unaffected by externally administered insulin. For individuals who take insulin as medication, a standard insulin test cannot distinguish between the body's own production and the injected dose. C-peptide sidesteps that problem entirely, providing a clean measurement of natural pancreatic output. Healthcare providers use the test to evaluate how well the pancreas is functioning, differentiate between type 1 and type 2 diabetes, assess insulin resistance, and monitor beta-cell function over time.
Who should consider this test
You might consider this test if you are experiencing any of the following:
- Individuals with diabetes who need to determine whether their pancreas is still producing insulin and may benefit from treatment adjustments.
- Those with newly diagnosed diabetes where the specific type (Type 1 or Type 2) is unclear and requires classification for proper treatment planning.
- People experiencing unexplained low blood sugar (hypoglycemia) episodes to help identify the underlying cause, such as excessive insulin production.
- Individuals suspected of having an insulin-producing tumor (insulinoma) or other pancreatic conditions affecting insulin production.
- Those with a family history of diabetes who want to assess their pancreatic function and insulin-producing capacity as part of early detection efforts.
What to expect
Preparation
You might need to fast, or stop eating, 8 to 10 hours before the test. Some providers may order the test after eating to evaluate how the pancreas responds to food. Inform your healthcare provider about all medications, including diabetes medications, as they may affect test results. No other special preparation is typically required.
Sample Type
During a blood test, a health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.
Collection
After checking in at the lab, a trained phlebotomist will clean the puncture site and draw blood from a vein in your arm. The sample is labeled and sent to the laboratory for analysis. The actual blood draw takes just a few minutes, and no doctor visit is required for this test.
Turnaround
Results of a C-peptide test can take one to five days, depending on the healthcare provider and lab. Results are typically available within 1-3 business days and will be sent directly to you through a secure patient portal.
Understanding your results
Normal C-peptide levels typically fall between 0.5 and 2.0 ng/mL (approximately 0.17 to 0.83 nmol/L), though reference ranges vary by laboratory. Results must be interpreted alongside the blood glucose level at the time of the draw, because C-peptide production naturally fluctuates in response to blood sugar: a low C-peptide paired with high blood sugar suggests the pancreas is struggling to produce adequate insulin, while a high C-peptide paired with high glucose may indicate insulin resistance. Healthcare providers use the relationship between these values, along with clinical symptoms and medical history, to assess pancreatic function and guide diabetes management.
| Population | Reference Range | Notes |
|---|---|---|
| Adults (Fasting) | 0.5-2.0 ng/mL (0.17-0.83 nmol/L) | Normal range for fasting C-peptide levels in healthy adults |
| Adults (After eating) | 1.0-3.0 ng/mL (0.33-1.0 nmol/L) | Expected range following meals when pancreas responds to increased glucose |
Reference ranges may vary by laboratory and individual factors. Results should be interpreted by a healthcare provider in the context of your overall health.
What does a “Low” result mean?
It can also mean that your body isn't making enough insulin or that you're taking insulin injections. Type 1 diabetes. Type 2 diabetes (if your pancreas is no longer producing insulin). Levels below 0.6 ng/mL (0.2 nmol/L) are a sign of possible beta cell failure and type 1 diabetes. Low C-peptide levels may also occur with severe infections, liver disease, or Addison's disease. For individuals taking insulin, low C-peptide may indicate that external insulin is suppressing the pancreas's natural insulin production.
What does a “High” result mean?
A high level of C-peptide might mean your body is making too much insulin. People with type 2 diabetes, obesity, or insulin resistance may have a high C-peptide level. This means their body is producing a lot of insulin to keep (or try to keep) their blood sugar normal. Elevated C-peptide levels may also be associated with kidney disease, as the kidneys typically clear C-peptide from the blood. In some cases, high C-peptide with low blood glucose may indicate an insulin-producing tumor (insulinoma), though this condition is uncommon.
Privacy & confidentiality
All C-peptide test results are kept strictly confidential and HIPAA-compliant. Results are not shared with insurance companies, do not appear on insurance EOBs, and are not automatically sent to your personal doctor unless you specifically request it.
Frequently asked questions
Related tests
Insulin Test
Measures insulin levels directly to complement C-peptide results for comprehensive diabetes evaluation
View TestGlucose Test
Essential for diagnosing diabetes and interpreting C-peptide results in clinical context
View TestA1C Test
Provides long-term blood sugar control information to complement C-peptide assessment of pancreatic function
View TestDiabetes Panel
Comprehensive testing including glucose, A1C, and other markers for complete diabetes evaluation
View TestRelated conditions
Last reviewed: April 2026
CPT Code: 84681
This test may not be available in: NY, NJ, RI
This page is for informational purposes only and does not constitute medical advice. Always consult with a healthcare provider regarding any health concerns. LevelPanel does not diagnose, treat, or prescribe.
Sources:
Order this test
Choose your preferred lab
LevelPanel has no business or affiliate relationship with Quest or LabCorp. These links are provided as a public service.
Lab testing services linked from this site are not available to residents of Alaska, Arizona, or Hawaii, unless otherwise noted on the lab's own website.
This publication is not intended to solicit the purchase of laboratory testing from any individual consumer.
Not sure if this is the right test? Contact our care team for guidance.
This page is intentionally kept stable and machine-readable so that researchers, clinicians, and AI systems can rely on it as a reference. See our Citation Policy.