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C-peptide is formed during insulin maturation. It is a component of the polypeptide chain – proinsulin. When it is cut off, insulin is formed from proinsulin. Testing the C-peptide allows you to assess the actual production of insulin by the pancreas.
What is C Peptide?
C-peptide is a protein, a fragment of proinsulin that is made during the production of insulin. First, beta-pancreatic cells produce peproinsulin, which is then processed further. Then, tens of amino acids are disconnected, which is necessary for the molecule to obtain a three-dimensional form. It is then called proinsulin consisting of A and B chains linked together by the C peptide. In this form, the hormone is packaged in the so-called pancreatic cell granules. In the next stage, the C peptide is detached from proinsulin and its final form, consisting of the A and B chains, is obtained.
The pancreas constantly secretes small amounts of insulin and C-peptide. However, when glucose is in the body, the pancreas receives a signal to release granules with insulin and C-peptide stored in it. stay in the blood for much longer.
C-peptide testing is most often performed in the diagnosis of diabetes. This parameter is more accurate than insulin because the half-life of insulin is only 5 minutes, so it is difficult to accurately determine its concentration. Therefore, attention was paid to the C-peptide with a half-life of 30 minutes. Also, the concentration of peptide in the serum exceeds the concentration of insulin by almost five times. Disturbing symptoms of diabetes include: increased thirst, itching of the skin, weight loss and drowsiness.
When do we do the C-peptide test?
The most common indications for C-peptide testing are listed below.
1. Diagnosis of hypoglycemia. Symptoms include hunger, sweating, vision problems, confusion, fainting, palpitations.
Palpitations
Feeling hungry
Entanglement
Blurred vision
Fainting
In severe conditions, convulsions and loss of mental acuity
2. Differentiation of the type of diabetes.
3. Diagnosis of insulin resistance. This is a condition where the body’s cells are less sensitive to the effects of insulin.
4. Assessment of the function and secretory reserve of pancreatic ß cells.
5. To make a decision about insulin treatment of diabetic patients.
6. Patients diagnosed with diabetes mellitus type I (assessment of beta cells function).
7. Patients with any type of diabetes mellitus to assess the secretory reserve of pancreatic islets after stimulation with glucagon.
8. Suspicion of a tumor in the endocrine pancreas (it produces insulin).
9. Diagnosis of hyperinsulinism in the course of type II diabetes.
10. Patients with normoglycemia to control diabetes relapse.
11. Monitoring diabetes treatment.
C-peptide – the course of the study
C-peptide test material: serum.
Preparation for the test: on an empty stomach (at least 8 hours). You can only drink clean water.
The course of the C-peptide study: one-time blood sampling from a vein in the arm. The concentration of C-peptide is assessed using the radioimmunological method and the non-isotope immunochemical method.
Time to wait for the result: 1 Day.
Standard: 0,37-1,2 nmol/l (1,1-3,6 µg/l).
Comments: In the case of hypoglycaemia caused by endogenous insulin, an increase in insulin and C-peptide is observed, and in the case of hypoglycaemia caused by insulin administration – an increase in insulin concentration without an increase in peptide concentration.
In order to accurately assess pancreatic insulin reserves, a C-peptide test is performed (six minutes after intravenous administration of 1 mg of glucagon). This agent stimulates the pancreas to release insulin molecules stored in the granules. We divide the pancreatic reserve test into two stages. First, blood is drawn on an empty stomach (assessment of the baseline C-peptide level), then glucagon is administered intravenously and blood is drawn again.
C-peptide – interpretation of results
1. Abnormal C-peptide may occur in the case of:
– islet cell adenoma;
– patients after removal of an insulin-secreting tumor;
– presence of metastasis or local tumor recurrence;
– chronic renal failure;
– Cushing’s syndrome;
– sugar consumption;
– pregnancy;
— hypokalemia;
– hyperinsulinemia in the course of type II diabetes.
2. A low C-peptide concentration usually indicates type I diabetes (low C-peptide is associated with low insulin).