C-peptide

C-peptide: role in the body, symptoms of deficiency and excess, norms in the blood test

The role of C-peptide in the body

C-peptide (connective peptideA peptide is a molecule consisting of a chain of amino acids linked together by peptide bonds. Peptides are shorter chains than proteins and usually contain from 2 to 50 amino acids. When the number of amino acids in a chain exceeds 50, such molecules are called proteins. Peptides can perform various functions in the body, including: Hormones, Neuropeptides, Antibiotics, Antioxidants) is a fragment of the proinsulin moleculethat is broken off during the formation of insulin in the beta cells of the pancreas. .Its level reflects the insulin-producing ability of the pancreas.

Main functions:

Marker of insulin synthesis (1 proinsulin molecule → 1 insulin molecule + 1 C-peptide molecule).
It helps to distinguish self-produced insulin from externally administered insulin(exogenous insulin does not contain C-peptide).
It is used to diagnose diabetes (especially if artificial hypoglycemia is suspected).
Evaluates the residual function of beta cells in patients with type 1 and type 2 diabetes.

Symptoms of C-peptide deficiency

A low level indicates insufficient insulinproduction, which occurs when:

Type 1 diabetes mellitus (autoimmune destruction of beta cells).
Long-term type 2 diabetes (depletion of pancreatic reserves).
Severe pancreatitis or removal of the pancreas.

Symptoms:

Hyperglycemia (high blood sugar).
Thirst, frequent urination.
Weight loss, weakness (with type 1 diabetes).
Ketoacidosis (with severe insulin deficiency).

Symptoms of excess C-peptide

An elevated level indicates an excessive production of insulin, which happens when:

Insulin resistance(type 2 diabetes, obesity).
Insulinoma (a hormone-active pancreatic tumor).
Renal failure (C-peptide is excreted by the kidneys, with their dysfunction, its level increases).
Taking sulfonylureas (stimulate the release of insulin).

Symptoms:

Hypoglycemia (low blood sugar): weakness, sweating, trembling, hunger.
Weight gain (due to hyperinsulinemia).
With insulinoma-attacks of hypoglycemia on an empty stomach.

Blood levels of C-peptide

Reference values depend on the analysis method and laboratory, but on average:

Condition	Norm (ng / ml)	Notes
On an empty stomach	0.8–4.2	In healthy people
After a meal	Up to 6-8	Peak in 1-2 hours
Type 1 diabetes	< 0.8	Reduced due to beta cell destruction
Type 2 diabetes	Increased or normal	Depends on the stage of the disease
Insulinoma	> 4-5 on an empty stomach	Diagnostic criteria

Important:

The test is taken on an empty stomach (8-12 hours of hunger).
For differential diagnosis , tests are performed with glucose or fasting.
The level of C-peptide does not depend on the injected insulin (unlike the insulin itself).

When is the test scheduled?

Differentiation of type 1 and type 2 diabetes.
Suspected insulinoma.
Control of residual beta cell function.
Suspicion of artificial hypoglycemia (secret use of insulin).