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C-Peptide

Hormones

C-Peptide

Also known as: Connecting Peptide

COMMON RANGE

1.1 – 4.4

ng/mL

4.8

Mayo Clinic Laboratories

Adult

↗

See all sources ↓

CONVERT & COMPARE

ng/mL

0.927

nmol/L

2.8

µg/L

2.8

mcg/L

2.8

ug/L

Reference ranges across 10+ sources

Adult reference ranges from 2 entries across 2 named sources, shown in ng/mL. Compare side-by-side.

SOURCE

SEX

AGE

RANGE

VISUAL

CITE

Mayo Clinic Laboratories

All

≥18y

1.1 – 4.4 ng/mL

↗

Labcorp

All

≥18y

0.4 – 2.1 ng/mL

↗

Mayo Clinic Laboratories

All · ≥18y

↗

1.1 – 4.4 ng/mL

Labcorp

All · ≥18y

↗

0.4 – 2.1 ng/mL

About C-Peptide

This test measures the level of C-peptide in a sample of your blood or urine (pee). C-peptide is a chain of amino acids (the building blocks of proteins) that your pancreas makes in the process of making insulin. Insulin is a hormone that your pancreas makes to help blood glucose (blood sugar) get into your cells, where it can be used for energy. This helps keep your blood glucose at healthy levels.

C-peptide and insulin enter your bloodstream at the same time and in equal amounts, but C-peptide stays in your blood longer. It is also unaffected by outside sources of insulin such as the medicines involved in diabetes treatment. In other words, C-peptide can give an accurate picture of how much insulin your body is making naturally.

Because of this, health care providers may rely on a C-peptide test to measure insulin levels rather than testing insulin levels directly.

Main source: MedlinePlus ↗

Useful for

Find the cause of hypoglycemia (low blood glucose). Some types of hypoglycemia are linked to high insulin levels, and by checking your C-peptide levels, your provider can tell whether this is the case.

Manage diabetes treatment. If you have type 1 or type 2 diabetes, treatment decisions may depend on knowing how much insulin your pancreas is making. A C-peptide test can provide an accurate measurement, even if you take insulin for diabetes. That's because your C-peptide levels depend only on how much insulin your pancreas makes.

Monitor treatment for a tumor in your pancreas, called an insulinoma (uncommon). These tumors make too much insulin and cause low blood glucose. They are almost always benign (not cancer) and can usually be removed with surgery.

Find out whether you have type 1 or type 2 diabetes if your diagnosis is uncertain. Usually, your health care provider can diagnose which type of diabetes you have without this test. But in certain cases, your provider may need to use a C-peptide test to make their diagnosis.

Main source: MedlinePlus ↗

Interpretation

The meaning of your results depends on your age, health, the medicines you take, and the results of other tests, such as a blood glucose test.

If you have been treated for an insulin-producing tumor in your pancreas, a decrease in your C-peptide levels means your treatment is working. An increase in your C-peptide may mean that your tumor is back.

If you have questions about your results, talk with your provider.

For general wellness information only. Talk to a clinician about your specific results.

Main source: MedlinePlus ↗

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Related biomarkers

Often tested alongside c-peptide or part of the same panel.

Thyroid Stimulating Hormone (TSH)

Hormones

Free T4 (Thyroxine)

Hormones

Free T3 (Triiodothyronine)

Hormones

Total T4 (Thyroxine)

Hormones

Total T3 (Triiodothyronine)

Hormones

Reverse T3 (rT3)

Hormones

Sources

Mayo Clinic Laboratories

Labcorp

Last updated 2026-05-02

This page aggregates publicly available reference data and clinical information from Mayo Clinic Laboratories and other sources. For general wellness information only — not medical advice. For diagnosis or treatment of any condition, talk to a qualified clinician.

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