"C-peptide" in translation from English means "connecting". It is considered an indicator of the production of own insulin and indicates the level of functionality of beta cells in the pancreas. These cells produce insulin, which is stored in the tissues of the pancreas, like proinsulin, in the form of molecules. In such molecules, a fragment (such as an amino acid residue) is located, which is called the C-peptide. In diabetes mellitus, with an increase in the concentration of glucose in the blood, proinsulin molecules begin to break down. The combination of peptide and insulin released into the blood always correlates with each other: within the normal range, this indicator is 5: 1.
What does this study reflect?
It is a laboratory study of the C-peptide that helps to understand that insulin production is reduced in the body, as well as to establish the possibility of developing insulinoma, which is a pancreatic tumor.
An increased concentration of this substance can be observed with:
- renal failure;
- diabetes insulin-dependent form;
- taking some hormonal drugs:
- the development of insulinomas;
- beta cell hypertrophy.
A low level of C-peptide is most characteristic for people suffering from an insulin-dependent form of diabetes mellitus with a hypoglycemic state, as well as for those who are in severe stressful conditions.
Study Features
A laboratory test for the level of C-peptide is the determination of the quantitative level of the protein part of proinsulin in the blood using the immunochemiluminescent method.
Initially, a pancreatic beta cell produces a passive insulin precursor, proinsulin, which is activated only when blood sugar levels increase by cleavage of protein components. Insulin molecules enter the bloodstream and circulate in it.
Analysis for C-peptide is carried out in order to:
- Indirectly determine the volume of insulin with inactivating antibodies that change indicators, namely, reducing them. The analysis is also carried out for severe violations of the liver.
- Define the category of diabetes and the main features of pancreatic beta cells in order to determine the therapeutic strategy.
- Identify the presence of tumor metastases from the pancreas after its surgical removal.
When is the analysis scheduled?
This blood test is prescribed for the following pathological processes:
- Type 1 diabetes, in which the protein concentration is lowered.
- Type 2 diabetes mellitus, in which this indicator exceeds the norm.
- Insulin-resistant diabetes mellitus as a result of the production of antibodies to insulin receptors - while the c-peptide is reduced.
- Condition after surgery to remove cancer of the pancreas.
- Infertility caused by a disease such as polycystic ovary.
- Gestational diabetes mellitus (potential risk for children is determined).
- A variety of disorders with pancreatic deformities.
- Somatotropinoma, in which the level of c-peptide rises.
- Cushing's Syndrome.
In addition, the determination of the specified substance in the blood will reveal the exact cause of the development of the hypoglycemic state in diabetes mellitus. This indicator increases significantly with the development of insulinoma, the use of sugar-lowering synthetic medications.
The level of C-peptide is lowered, as a rule, after drinking high doses of alcohol or against the background of the introduction of exogenous insulin to diabetics on an ongoing basis.
What are the symptoms of this study?
A laboratory test is prescribed if the patient complains of the following symptoms:
- constant thirst;
- increased urine output;
- weight gain.
If a person already has a diagnosis of diabetes mellitus, then the level of this substance is determined in order to assess the quality of ongoing therapeutic measures. Incorrect treatment can lead to the development of chronic forms of the disease, most often in this case, patients complain of rapid visual impairment and decreased sensitivity of the lower extremities.
In addition, symptoms of impaired renal function and the development of arterial hypertension may be noted.
Features of the procedure
For laboratory analysis, venous blood is taken into a plastic container. For eight hours before the test, the patient should not eat, but it is allowed to drink water.
It is advisable not to be subjected to heavy emotional and physical stress, and not to smoke several hours before the start of the procedure. In some cases, you need to contact an endocrinologist to correct insulin therapy. The result of the study can be known after 3 hours.
What is the normal C-peptide in the blood?
Interpretation of analysis and norm
In terms of the norm, this indicator is the same for women and men. It does not depend on the age of the patients and is approximately 0.9 - 7.1 ng / ml. The norm for children in a particular case is determined by the doctor.
As a rule, the dynamics of indicators in the blood corresponds to insulin dynamics. The norm of the C-peptide in the morning, before meals, is 0.78 -1.88 ng / ml.
For children, the basic rules for taking blood do not change. However, this substance in a child during an empty stomach test may be slightly lower than the lower limit of the normal indicator, since the C-peptide enters the blood from beta cells only after eating. If all other diagnostic studies do not show signs of the development of a pathological process, then such a change in the indicator should not cause concern.
In order to distinguish between insulin and actual hypoglycemia, it is necessary to determine the ratio of insulin concentration to C-peptide concentration. If this ratio is 1 or less, then this indicates an increase in the production of endogenous insulin. In cases of exceeding the ratio of 1, it is safe to say that insulin was ingested from the outside.
Reasons for the increase
C-peptide increases in the following cases:
- hypertrophy of the cells of the islets of Langerhans, which are areas of the pancreas in which insulin is produced;
- obesity;
- insulinoma;
- type 2 diabetes;
- oncology of the head;
- oncology of the head of the gland;
- extended QT interval syndrome;
- the use of sulfonylurea medications.
In addition to the above cases, it can be increased when the patient uses certain types of hypoglycemic drugs and estrogens.
Reasons for the decline
The level of C-peptide is reduced in the following cases:
- alcoholic hypoglycemia;
- type 1 diabetes;
- the use of thiazolidinediones, for example, rosiglitazone or troglitazone.
As a result of insulin therapy, a decrease in the concentration of this indicator may be observed. This may indicate healthy reactions of the pancreas to the formation of "artificial" insulin in the body.
However, it often happens that the concentration in the blood of this peptide on an empty stomach is normal or is in the extremes of normal. This means that the norm indicator cannot indicate which type of diabetes the patient has. Based on this, a special stimulated test should be carried out, which shows the norm of the substance for this patient. It is carried out using:
- injections of glucagon (an insulin antagonist), which is strictly contraindicated in patients with pheochromocytoma or hypertension;
- glucose tolerance test.
The best option would be to determine two studies: an empty stomach test and a stimulated test. Now different laboratories use different kits to study the level of the substance, and the standards may vary slightly. Having received the results of the study, the patient can compare them with reference indicators.
C-peptides in diabetes
In modern clinical medicine, it is believed that monitoring the level of this indicator clearly reflects the concentration of insulin.
Another advantage is that using research, you can distinguish between endogenous insulin and exogenous. Compared to insulin, the C-peptide does not respond to antibody levels and is not destroyed by such antibodies. Since insulin preparations do not contain this substance, its level in the blood of a diabetic makes it possible to evaluate the functionality of beta cells.
In a patient with diabetes mellitus, basal levels of this molecular compound and its concentration after glucose intake make it possible to find out whether there is sensitivity and resistance to insulin.
Thus, we examined what the C peptide shows.