Why this test?
To assess the level of insulin secretion by β-cells of the pancreas when diabetes is suspected;
To assess the effect of treatment on preserving the residual function of β-cells of the pancreas and to assess the prognosis of type 1 diabetes;
To detect a significant decrease in the function of β-cells of the pancreas and timely start of therapy with insulin drugs in patients with type 2 diabetes;
For the diagnosis of insulinoma, as well as combined tumors of the pancreas.
In what cases is it prescribed?
In the presence of symptoms of severe hyperglycemia of type 1 diabetes: thirst, increased daily urine volume, weight gain, increased appetite;
in the presence of symptoms of moderate hyperglycemia of type 2 diabetes: visual impairment, dizziness, weakness, especially in overweight or obese individuals;
in the presence of symptoms of chronic hyperglycemia: a progressive decrease in vision, a decrease in the sensitivity of the limbs, the formation of ulcers on the lower limbs that do not heal for a long time, the development of chronic kidney failure, coronary heart disease and arterial hypertension, especially in people with excess body weight or obesity;
during differential diagnosis of type 1 and type 2 diabetes, especially in the case of diagnosis of diabetes in children and young people;
at the control stage of type 1 diabetes mellitus treatment;
in the need to start insulin therapy in patients with type 2 diabetes who cannot achieve optimal glucose levels with the help of a combination of hypoglycemic drugs in the maximum possible therapeutic doses;
in the presence of symptoms of hypoglycemia with insulinoma: anxiety, palpitations, increased sweating, dizziness, hunger, impaired consciousness, memory, sleep and psyche.
C-peptide (from the English Connecting peptide - "connecting", "connecting peptide") is so named because it connects the alpha and beta peptide chains in the proinsulin molecule. This protein is necessary for the synthesis of insulin in the cells of the pancreas - a multi-stage process, at the final stage of which the inactive proinsulin is split with the release of active insulin.
As a result of this reaction, an amount of C-peptide equal to insulin is also formed, which is why this laboratory indicator is used to estimate the level of endogenous insulin (the concentration of insulin itself is rarely measured for this purpose). This is due to the peculiarities of insulin metabolism in normal conditions and in pancreatic pathology. After secretion, insulin with the flow of portal blood is sent to the liver, which accumulates a significant part of it ("first-pass effect"), and only then enters the bloodstream.
As a result, the concentration of insulin in the venous blood does not reflect the level of its secretion by the pancreas. In addition, the level of insulin varies significantly in many physiological states (for example, eating stimulates its production, and it is reduced during fasting). Its concentration also changes in diseases accompanied by a significant decrease in the level of insulin (diabetes).
When autoantibodies to insulin appear, conducting chemical reactions for its determination is quite difficult. Finally, if recombinant insulin is used as replacement therapy, it is not possible to distinguish between exogenous and endogenous insulin. Unlike insulin, C-peptide does not have a "first-pass effect" in the liver, so the concentration of C-peptide in the blood corresponds to its production in the pancreas. Since C-peptide is produced in equal ratio with insulin, the concentration of C-peptide in the peripheral blood corresponds to the direct production of insulin in the pancreas. In addition, the concentration of C-peptide does not depend on changes in the level of glucose in the blood and is relatively constant. These features allow us to consider the C-peptide analysis the best method to assess insulin production in the pancreas.
Normally, insulin is produced in the beta cells of the pancreas in response to an increase in blood glucose concentration. This hormone performs many functions, the main one of which, however, is ensuring the supply of glucose to insulin-dependent tissues (in the liver, fat and muscle tissue). Diseases in which there is an absolute or relative decrease in the level of insulin, disrupt the utilization of glucose and are accompanied by hyperglycemia. Despite the fact that the causes and mechanisms of development of these diseases are different, hyperglycemia is a common metabolic disorder that determines their clinical picture; this is a diagnostic criterion for diabetes. There are type 1 and type 2 diabetes, as well as some other syndromes characterized by hyperglycemia (MODY-diabetes, gestational diabetes, etc.).
Detection of elevated C-peptide helps in the diagnosis of insulinoma and can be used in combination with others laboratory and instrumental methods. It should be noted that insulinoma is a component of multiple endocrine neoplasia syndrome, and can also be combined with another tumor of the pancreas - gastrinoma"