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C-peptide (Serum or Plasma) with 24-Hour Urine Collection for Measurement

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

This test measures C-peptide, a natural byproduct of insulin production, to assess how well your pancreas is making insulin. It’s often used to evaluate diabetes management or rule out insulin use.

Quick summary

["C-peptide helps track natural insulin production, not artificial sources like insulin injections."]

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

Key facts at a glance

LOINC
47589-7
Short code
C peptide 30M p Glc SerPl-sCnc
Synonyms
C peptide 30M p Glc SerPl-sCnc
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

Why This Test Matters for Diabetes Care

C-peptide is a key marker for understanding whether your diabetes is managed by your own pancreas or requires external insulin. Unlike insulin levels, C-peptide reflects natural insulin release, helping doctors distinguish between type 1 and type 2 diabetes and monitor treatment effectiveness.

How the Test Works

Your blood (serum or plasma) and a 24-hour urine sample are collected to measure C-peptide levels. The test checks how much C-peptide your body produces naturally, which correlates with insulin output.

What the Results Mean

Lower-than-expected C-peptide may indicate insufficient natural insulin production (common in type 1 diabetes or advanced type 2). Higher-than-expected levels could suggest overproduction or other metabolic conditions. Results help guide treatment plans.

Common Reasons for Testing

Doctors may order this test if you have diabetes symptoms, unexplained weight changes, or if insulin use is suspected (e.g., after a suspected insulin overdose). It’s also used to confirm diabetes type or assess pancreatic function.

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 monitoring

Frequently asked questions

Why might my doctor want to check my C-peptide levels?
Your doctor may recommend this test to confirm whether your diabetes is caused by insufficient insulin production (type 1) or insulin resistance (type 2). It helps rule out insulin misuse, monitor treatment success, or evaluate pancreatic health in conditions like pancreatitis.
What should I expect during the test?
You’ll have a blood draw (like a regular lab test) and provide a 24-hour urine sample in a container. No special prep is needed, but drink plenty of water to help urine flow. Results take 1–3 days.
Can C-peptide test results change over time?
Yes, C-peptide levels can fluctuate with diet, exercise, stress, or medications. If your results vary, discuss them with your doctor to understand potential causes, such as changes in diabetes management or underlying health conditions.
  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