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In the human body, C-peptide is a certain indicator by which experts see the level of synthesis of their own (endogenous) insulin and carbohydrate metabolism. With the help of a blood test for C-peptide, specialists diagnose types 1 and 2 diabetes mellitus, insulinoma, evaluate the level of insulin secretion in liver pathologies and the effectiveness of insulin therapy.
Characteristics of the determined indicator
In medicine, the C-peptide is understood to be the protein component of the proinsulin molecule, upon cleavage of which insulin is synthesized. With an increase in blood glucose levels, proinsulin is split into C-peptide and insulin with parallel secretion of an equimolar amount of substances into the blood. In this case, the C-peptide is formed according to a certain pattern.
Proinsulin contains a polypeptide chain of 84 amino acid residues. At the same time, proinsulin does not have hormonal activity. Proinsulin is synthesized in the human body in the pancreatic islets in fractions of microsomes of beta cells. Inactive proinsulin is converted to active insulin during its movement to secretory granules from ribosomes via partial proteolysis. During this process, the C-peptide is cleaved from the C-terminus of the polypeptide chain with 33 amino acid residues. The original structure and length of the C-peptide varies greatly in different animals, in contrast to the sequence of insulin chains A and B.
At the same time, despite the lack of biological activity of the C-peptide, it is able to reflect the rate of insulin production in the human body. It should be understood that all of the above does not mean the same half-life of C-peptide and insulin in human blood. These parameters are different, however, the correlation between their presence in the blood test with non-matching serum concentrations is quite pronounced. That is why, when determining the presence and concentration of C-peptide, it becomes possible to talk about the concentration of own insulin in the blood during insulin therapy.
The C-peptide indicator in a blood test helps doctors find out the causes of hypoglycemia in the human body, that is, to carry out differential diagnosis of types 1 and 2 diabetes mellitus. Also, this analysis indirectly visualizes the insulin level in the blood in the presence of antibodies to it, reveals the remnants of pancreatic tissues during pancreatectomy performed to diagnose oncological processes in the pancreas, and helps patients with diabetes to determine the functions of beta cells in pancreatic islets.
Conducting an analysis to determine the indicator
A patient’s blood test for C-peptide is taken in cases where specialists need to:
- differential diagnosis of 1 and 2 types of diabetes mellitus;
- differential diagnosis of hypoglycemia states;
- determination of tactics for the treatment of diabetes mellitus;
- assessment on the eve of insulin therapy of residual functions of beta cells and control of remission processes in the elimination of hyperglycemia;
- dynamic control in surgical treatment of the pancreas;
- examination for polycystic ovaries in all patients.
A blood test for C-peptide occurs according to a certain pattern. After the venipuncture, blood is taken into a test tube.
Blood after taking is subjected to centrifugation and subsequent freezing, so that it is possible to analyze at a later date. When the analysis for the indicator in question is passed, the patient returns to his usual lifestyle – diet and medication.
The analysis itself is given in the morning on an empty stomach. The day before, the patient is advised not to eat for 6-8 hours. All this time you can only drink clean water. Such measures are taken because the analysis will evaluate the functioning of the patient’s pancreas.
At the same time, the patient should not use drugs the day before that can distort the results of the tests, and if it is impossible to refuse them, this information must be indicated in the test forms.
What do the test scores show?
An endocrinologist should refer the patient to a blood test for C-peptide. The indicators identified during the analysis will be able to tell a lot about the specialist in the future. For example, an increase in C-peptide indicates food intake, an increase in the number of beta cells, kidney failure, insulinoma, non-insulin-dependent type 2 diabetes mellitus, hypoglycemia when the patient takes oral glucose-lowering drugs (sulfonylurea derivatives), transplantation of β-cells or pancreas.
A reduced rate of C-peptide indicates a normal reaction of the pancreas in response to insulin administration, alcoholic hypoglycemia, a state of stress, or the patient is diagnosed with type 1 diabetes mellitus (insulin-dependent diabetes).
Thus, experts say that a blood test to determine the level of C-peptide is the most important point in the diagnosis of many diseases, during which it is very important to timely determine the level of increase and decrease in insulin in the blood.