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C-peptide (Serum/Plasma, Quantitative)

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

This test measures the amount of C-peptide, a small protein produced along with insulin when your pancreas releases it to regulate blood sugar.

Quick summary

["C-peptide helps doctors assess how well your pancreas is producing insulin naturally."]

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

Key facts at a glance

LOINC
57645-4
Short code
C peptide 10M pre chal SerPl-sCnc
Synonyms
C peptide 10M pre chal SerPl-sCnc
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

Your doctor may order a C-peptide test to evaluate your pancreas’s function, especially if you have diabetes or symptoms like unexplained weight loss, fatigue, or high blood sugar. It can also help distinguish between types of diabetes or check for insulin-producing tumors.

What to Expect Before the Test

No special preparation is needed. You may have a small needle inserted into your arm or vein to draw a blood sample. If fasting is required (sometimes for related tests), follow your doctor’s instructions.

What the Results Mean

Results help determine if your pancreas is making insulin normally. Low levels may suggest diabetes or insulin deficiency, while high levels could indicate overproduction of insulin (e.g., from a tumor). Your doctor will interpret results in the context of your symptoms and medical history.

Common Reasons for Testing

C-peptide testing is often used alongside insulin levels to diagnose diabetes types (e.g., Type 1 vs. Type 2) or rule out conditions like insulinoma (a rare tumor causing excessive insulin). It’s also useful in monitoring pancreatic health in chronic diseases.

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

How long does it take to get results from this test?
Results are typically ready within 1–3 business days, depending on your lab. Your doctor will discuss them with you during your follow-up visit.
Can fasting affect C-peptide test results?
Fasting may not significantly alter C-peptide levels, but if your doctor ordered additional tests (like fasting glucose), follow their fasting instructions carefully.
Is C-peptide testing painful?
Most people experience only mild discomfort from a small needle stick. If you’re anxious, ask your doctor about numbing cream or other options.
  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