From the Guidelines
C-peptide is a protein fragment produced during insulin production in the pancreas, and measuring it in the blood provides valuable information about how much insulin a person's pancreas is producing naturally, which is crucial for distinguishing between type 1 and type 2 diabetes, evaluating insulin production in diabetic patients, and determining if high insulin levels are due to excessive pancreatic production or external insulin administration 1.
Key Points
- C-peptide is a byproduct of insulin production, released into the bloodstream in equal amounts to insulin.
- Measuring C-peptide levels helps determine the pancreas's natural insulin production, which is essential for diagnosing and managing diabetes.
- C-peptide testing is particularly useful in ambiguous cases, such as distinguishing between type 1 and type 2 diabetes, especially when clinical presentation and subsequent course are unclear 1.
- Normal C-peptide levels indicate proper insulin production, while low levels may suggest type 1 diabetes, and high levels can indicate insulin resistance as seen in type 2 diabetes.
Clinical Applications
- C-peptide measurement can aid in diagnosing type 1 diabetes, especially in adults with suspected type 1 diabetes, as outlined in the flowchart for investigation of suspected type 1 diabetes in newly diagnosed adults 1.
- C-peptide testing is recommended in people receiving insulin treatment, with a random sample or formal C-peptide stimulation test, to determine the level of insulin production and guide treatment decisions 1.
- C-peptide levels can also help evaluate insulin production in diabetic patients and determine if high insulin levels are due to excessive pancreatic production or external insulin administration.
Evidence-Based Recommendations
- The most recent and highest-quality study recommends using C-peptide measurements to distinguish between type 1 and type 2 diabetes in ambiguous cases, with a level of evidence rated as moderate 1.
- The American Diabetes Association recommends measuring C-peptide levels in people with suspected type 1 diabetes, especially in adults, to guide diagnosis and treatment decisions 1.
From the Research
Definition and Function of C-Peptide
- C-peptide is a protein that joins insulin's α and B chains in the proinsulin molecule 2.
- It is cleaved from proinsulin and secreted in an equimolar concentration to insulin from the β cells 2.
- C-peptide may be used as a marker of endogenous insulin production and a reflection of β-cell function 2.
Biological Properties and Effects
- C-peptide has important biological properties and displays beneficial effects in many tissues affected by diabetic complications 3.
- It has been shown to increase peripheral blood flow and protect from renal damage 3.
- C-peptide interacts with cellular membranes at unidentified sites distinctive of the insulin family of receptors, and signals to multiple targets known to play a role in diabetes and diabetic complications 3.
Clinical Applications and Utility
- C-peptide may lend itself to clinical applications, particularly in the management of type 1 and type 2 diabetes 3, 4, 5.
- Measurement of endogenous insulin secretion using fasting C-peptide is recommended as a diagnostic criterion for type 1 diabetes 5.
- C-peptide levels may be used to predict future outcomes in type 2 diabetes and to indicate the need for insulin therapy 4, 5.