C-peptide testing

What is C-peptide?

C peptide originates in pancreatic beta cells as a byproduct of enzymatic cleavage of pro-insulin to insulin .C-peptide is a connecting peptide that gets released alongside insulin from the pancreas. While insulin helps usher glucose (sugar) from the bloodstream into cells for energy, C-peptide itself has no known function in the body.

C-peptide and insulin are produced in equal amounts, and C-peptide has a longer half-life than insulin, making it easier to measure and serve as a valuable index to insulin secretion .

 In presence of anti – insulin antibodies C peptide concentrations reflect  the endogenous pancreatic insulin secretion reliably than insulin itself.  

Why is a C-peptide test performed?

There are several reasons why a doctor might order a C-peptide test:

  • Diagnosing type 1 vs. type 2 diabetes: In type 1 diabetes is a autoimmune disorder that attacks insulin-producing beta cells in the pancreas, leading to very low or undetectable C-peptide levels. In type 2 diabetes, the body either doesn’t produce enough insulin or becomes resistant to its effects. C-peptide levels can be helpful in differentiating between the two types.
  • Monitoring diabetes treatment: C-peptide levels can help assess the effectiveness of diabetes treatment plans, particularly in patients taking medications that stimulate insulin production.
  • Investigating low blood sugar (hypoglycemia): Extremely low C-peptide levels along with hypoglycemia can suggest problems with insulin production, helping pinpoint the cause.
  • Evaluating pancreatic function: C-peptide testing can aid in diagnosing pancreatic disorders that might affect insulin production.

Clinical uses can be summarise as

  1. Differentiating latent autoimmune diabetes of adults and type 2 diabetes mellitus.
  2. Diagnosis and monitoring of insulinoma ( pancreatic tumor)
  3. Diagnosis of factitious hypoglycemia
  4. Monitoring islet cell transplant
  5. C-peptide is extremely useful in the differential diagnosis of hyperinsulinemic-hypoglycemia.


Increased levels of C-peptide can seen in

Type 2 diabetes, renal insufficiency , obesity, Insulinoma.

Decreased levels of C-peptide can seen in

Exogenous insulin administration, Type 1 diabetes, pancreatectomy ,chronic pancreatitis.


This test may exhibit interference when the sample is collected from a person who is consuming a high dose of biotin (>5mg/day) Patients should be cautioned to stop biotin consumption at least 8 hours before collection of the sample.

In rare cases heterophile antibodies in serum can react with reagent immunoglobulin and cause interference in results, particularly seen in persons exposed to animals and animal serum products .


Wallach’s interpretation of diagnostics tests, 12th edition.

Sacks DB. Chapter 24: Carbohydrates. In: Burtis CA, Ashwood ER (eds). Tietz Textbook of Clinical Chemistry, WB Saunders, Philadelphia, 3rd edition;1999:750-808

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