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C-peptide (Serum or Plasma) – Quantitative

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

This test measures the amount of C-peptide, a small protein produced by your pancreas along with insulin during digestion. 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
13042-7
Short code
C peptide 2.5h p chal SerPl-mCnc
Synonyms
C peptide 2.5h 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 This Test Is Done

Doctors may order a C-peptide test to check if your body produces enough insulin independently of medication. It can help determine whether diabetes is caused by the pancreas not making insulin (Type 1 diabetes) or by insulin resistance (Type 2 diabetes). It’s also used to monitor treatment progress in people with diabetes.

What to Expect Before the Test

No special preparation is needed for this blood test. You may have a small needle inserted into your arm or hand to draw a blood sample. If you’re fasting, follow your doctor’s instructions, but fasting isn’t required for this test.

What the Results Mean

High levels of C-peptide may suggest your body produces insulin naturally, even if you have diabetes. Low levels could indicate the pancreas isn’t making enough insulin. Your doctor will interpret results in the context of your medical history and symptoms.

Common Conditions Linked to C-peptide Testing

This test is often used to diagnose or confirm diabetes, especially when insulin resistance or other factors are suspected. It may also be checked in people with unexplained weight loss, nausea, or symptoms of low blood sugar (hypoglycemia).

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.

Clinical Significance

Short name

C-peptide level

Frequently asked questions

What does a high C-peptide level mean?
A high C-peptide level may indicate your body produces insulin naturally, even if you have diabetes. This could suggest Type 2 diabetes with some insulin production or a condition like acromegaly, where hormone levels affect metabolism.
What does a low C-peptide level mean?
A low C-peptide level often means your pancreas isn’t producing enough insulin, which can be a sign of Type 1 diabetes or severe insulin resistance. It may also occur in cases of severe pancreatic damage or certain genetic disorders.
How is C-peptide different from insulin levels?
C-peptide is a marker of natural insulin production because it’s released in equal amounts with insulin. Unlike insulin, which can be affected by medications or stress, C-peptide levels reflect your body’s own insulin-making ability.
  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