C-peptide measured by high-performance liquid chromatography (HPLC) in serum/plasma
This test measures C-peptide, a small protein produced equally by your pancreas when insulin is made, helping assess how well your pancreas is producing insulin naturally.
["C-peptide helps evaluate pancreatic function and insulin secretion independently of blood insulin levels."]
Key facts at a glance
- LOINC
- 58686-7
- Short code
- C peptide 2h p Glc SerPl-mCnc
- Synonyms
- C peptide 2h p Glc SerPl-mCnc
- Category
- glucose
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 0.8
- Ref high
- 1.2
- Critical range
- — – 5 N/A
- Fasting
- true
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 85610
- SNOMED
- 396252006
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
Your doctor may order this test to find out how much insulin your pancreas is producing, to help explain why your blood sugar is too high or too low, or to monitor certain conditions that affect insulin production.
Doctors may order this test to diagnose or monitor conditions like diabetes, especially Type 1 diabetes where the pancreas produces little to no insulin. It can also help determine if insulin therapy is working properly by checking natural insulin production levels.
This test measures the level of C-peptide in your blood, a substance released alongside insulin when your pancreas makes it, which helps show whether your body is producing enough insulin on its own.
C-peptide is a byproduct of insulin production. Unlike insulin, it circulates in your blood at a steady level, regardless of whether you’re taking insulin or not. Measuring it helps separate natural insulin production from external sources like insulin injections or medications.
A small blood sample is drawn from a vein in your arm. You may be asked to fast for 8 to 10 hours before the test, so scheduling it in the morning and drinking only water beforehand is often recommended.
This test uses a blood sample drawn from a vein, typically in a clinic or lab. The blood is processed to separate serum or plasma, which is then analyzed using HPLC to measure C-peptide concentration precisely.
Tell your doctor about any medicines or supplements you take, since some can affect your results. Follow any fasting instructions you are given, and plan to relax for a few minutes before the blood draw.
No special preparation is needed for this test. You may eat and drink normally, but avoid smoking or drinking alcohol right before your blood draw if instructed by your healthcare provider.
Reference range
INR: 0.8-1.2 (warfarin: 2.0-3.0)N/A
Inform your healthcare provider if you are taking blood thinners. No special preparation required.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
C-peptide (HPLC)
Frequently asked questions
C-peptide levels are critical in diagnosing diabetes, especially Type 1, where the pancreas fails to produce insulin. High levels may indicate overproduction of insulin (e.g., insulinoma), while low levels suggest insufficient natural insulin production. It’s also useful in monitoring patients on insulin therapy to ensure their body isn’t relying too much on external insulin.
A low C-peptide level often suggests that your pancreas isn’t producing enough insulin naturally, which can be seen in Type 1 diabetes or severe insulin deficiency. It may also indicate that you’re on insulin therapy and your body isn’t producing insulin on its own.
C-peptide is a marker of natural insulin production because it’s released along with insulin. Unlike insulin, which can be affected by insulin injections or medications, C-peptide levels reflect your body’s own insulin-making ability.
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy