C-peptide

The C- peptide ( engl. connecting peptide) is part of proinsulin and laboratory- determined primarily in the differential diagnosis of diabetes mellitus, but also for the diagnosis of an insulinoma or a factitious hypoglycaemia.

Construction

The C peptide consisting of 31 amino acids and connects the A- chain to the B - chain of the proinsulin. In the conversion of proinsulin to insulin that is enzymatically cleaved in order to be then distributed along with insulin from β - cells of the pancreas into the bloodstream. C-peptide has its own effects on carbohydrate metabolism and its absence may play a role in the development of diabetic organ damage. In drug administered insulin the C-peptide is no longer available.

Proof

The C-peptide can be detected by laboratory diagnosis in serum or urine by an enzymatic immunoassay. The half-life of C-peptide is ten times longer than that of insulin.

Indication

C-peptide serves as a marker (measured value ) of the secretion of the β - cells of the pancreas. As part of a glucose tolerance test can their responsiveness can be determined.

Interpretation

• Diabetes mellitus type 1, for example, also LADA
• Diabetes mellitus type 2 in case of failure of insulin production in the late stage of the disease

• Type 2 diabetes mellitus as a sign of insulin resistance
• Insulinoma

• Hypoglycaemia factitia in the context of Munchausen syndrome.

To determine the need for insulin a diabetic, the ratio of C - peptide to fasting blood glucose ( FBG ) can be determined. Values ​​below 11.7 speak for a secondary failure and the need for insulin administration.

The glucose tolerance test is used to determine the glucose stability. For this purpose, after intravenous bolus injection of glucose, the increase in C- peptide are measured ( glucose). Case of a missing or only a small increase fluctuations in blood glucose levels despite intensive therapy and good patient compliance (compliance) are likely.

Summary

The presence of C- peptide in the blood gives information on the state of the body's insulin production. The C -peptide amount is directly proportional to the undistributed insulin. The significance of diabetes mellitus in slightly decreased values ​​is low. Only the absolute lack or markedly reduced levels (below 0.5-1.0 g / l) correlated with a substitution requiring insulin deficiency symptoms. By contrast, may also be necessary if increased levels of insulin therapy due to insulin resistance. With a drop below the normal range, an insulin therapy, perhaps even if only low doses are started, as at even low self- release of insulin, the survival of functional β - cells is prolonged by the early exogenous insulin administration. So far as the height of the C-peptide level has a prognostic value in the course of diabetes disease.

When insulinoma C-peptide plays an important role in the diagnosis of disease and may later serve as a tumor marker.

It supports the detection of factitious hypoglycaemia.