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C-peptide (Serum)

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of C-peptide, a small protein produced by your pancreas when it releases insulin. It helps assess how well your pancreas is producing insulin naturally.

Quick summary

["C-peptide helps diagnose and monitor diabetes and pancreatic function."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
27421-7
Short code
C peptide 40M p chal SerPl-mCnc
Synonyms
C peptide 40M p chal SerPl-mCnc
Category
coagulation
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
0.8
Ref high
1.2
Critical range
— – 5 N/A
Fasting
false
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

Why Is This Test Done?

Your healthcare provider may order a C-peptide test to check if your body produces enough insulin on its own, especially if you have diabetes or unexplained weight loss. It can also help determine if insulin injections are needed or if your pancreas is functioning normally after surgery.

What to Expect Before the Test

No special preparation is usually needed. You may be asked to fast for 8–12 hours before the test, but this depends on your doctor’s instructions. Bring any medications you’re taking to your appointment.

What Happens During the Test?

A small needle will draw blood from a vein in your arm. You may feel a slight pinch, but it’s quick. The blood sample is sent to a lab for analysis.

What Do Results Mean?

Results help doctors understand insulin production. Low levels may indicate diabetes or poor pancreas function, while normal levels suggest healthy insulin release. Your doctor will interpret results in the context of your medical history.

Reference range

INR: 0.8-1.2 (warfarin: 2.0-3.0)N/A

Specimen: serum

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 Level

Frequently asked questions

Why might my doctor ask for this test?
Your doctor may order it to evaluate your pancreas’s ability to produce insulin, especially if you have symptoms like unexplained weight loss, frequent infections, or if you’ve recently been diagnosed with diabetes. It can also help guide treatment decisions, such as whether you need insulin injections.
What are typical reference ranges?
Reference ranges vary by lab, but healthy levels are usually between 0.5–2.5 nanograms per milliliter (ng/mL). Your doctor will provide your specific results and explain what they mean for you.
Can fasting affect my C-peptide results?
Yes, fasting can influence C-peptide levels. If your doctor asks for fasting, it’s important to follow their instructions to get an accurate reading. Non-fasting results may not reflect your normal insulin production.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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