Quick Facts
- Sample: Blood serum
- Fasting: Fast for 14–16 hours before testing; drink only water during the fasting period. Stop biotin supplements 72 hours before collection and do not stop prescribed medications unless instructed by your healthcare provider.
- Turnaround: 1-2 business days. May take longer based on weather, holiday, or lab delays.
What This Test Measures
This test measures the level of C-peptide in your blood serum. C-peptide is released by your pancreas in equal amounts alongside your body's own insulin, but it remains in circulation longer, which makes it a useful marker of your natural insulin production. Because C-peptide is only produced by your pancreas and not found in injected insulin, this test reflects your endogenous insulin output specifically, even if you currently use insulin therapy.
This is a single fasting blood draw, not a timed or multi-specimen protocol. The result reflects your C-peptide level at the time of collection and does not directly measure blood glucose, total or free insulin, or insulin resistance.
Benefits
- Reflects your natural insulin production, even if you use insulin therapy
- May help investigate unexplained episodes of low blood sugar
- Offers an alternative to direct insulin testing for people with insulin antibodies
- Supports evaluation of suspected insulinoma or pancreatic tumors
- Can be ordered online without an in-person doctor's visit
- Useful for tracking pancreatic function over time when repeated
Who Is This Test For?
- Adults with diabetes who want insight into their body's own insulin production
- People on insulin therapy who want to assess their remaining pancreatic function
- Individuals experiencing unexplained episodes of low blood sugar
- People whose healthcare provider is evaluating their diabetes classification
- Those with a family history of diabetes interested in their insulin production
- Individuals being evaluated for a possible insulinoma or pancreatic tumor
How It Works
- Order Your Test Online
- Visit a Local Lab
- Get Results Online
FAQ
1. Do I need to fast or prepare for this test?
Fasting is required for this test: avoid food for 14 to 16 hours beforehand, drinking only water during that window. Stop taking biotin supplements at least 72 hours before your blood draw, since biotin can interfere with the result. Do not stop prescribed medication unless instructed by your healthcare provider.
2. How quickly will I get results?
Lab processing typically takes 1 to 2 business days from the time your sample is received. Weather events, holidays, or unexpected lab delays can occasionally extend this window, so treat the estimate as a general guide rather than a fixed date.
3. What can my results tell me?
A C-peptide level gives you a snapshot of how much insulin your pancreas is producing on its own at the time of the draw. It can offer context when investigating low blood sugar or when a healthcare provider is piecing together a broader picture of your insulin production, but it does not by itself provide a complete diabetes evaluation or confirm a specific diagnosis.
4. What factors can affect my results?
Not fasting for the full 14 to 16 hours can alter your result, as can taking biotin supplements within 72 hours of your draw. Insulin therapy and certain diabetes medications may also affect your natural insulin secretion, which in turn can influence your C-peptide level, so it's worth telling the lab about any medications you're taking.
5. How do I interpret the results?
Interpreting a C-peptide level depends on your fasting status at collection, your medication use, and the broader clinical picture, so it's best reviewed alongside other testing and your medical history. A single high or low value does not, on its own, confirm or rule out diabetes, insulin resistance, or a specific diabetes type. Bring your results to a qualified healthcare provider for guidance tailored to your situation.
Disclaimer: Reference ranges may vary by laboratory. Listed ranges are general guidelines and may differ from those used by the performing lab. Always consult your healthcare provider for interpretation.
6. What should I do if my results are abnormal?
Share an unexpected result with a qualified healthcare provider rather than trying to interpret it on your own. An abnormal C-peptide level doesn't automatically mean you have diabetes, insulin resistance, or a pancreatic condition, and it doesn't call for any change to your medication on its own. Your provider can determine whether additional testing or evaluation makes sense based on your full health picture.
Pre-test preparation
Fast for 14 to 16 hours before your test, drinking only water during this period. Discontinue biotin supplements at least 72 hours before your collection, as biotin can interfere with results. Do not stop prescribed medication unless instructed by your healthcare provider. Scheduling your appointment in the morning can make the fasting window easier to manage.
