C-peptide

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

construction

The C-peptide consists of 31 amino acids and connects the A chain with the B chain of proinsulin . When proinsulin is converted to insulin, it is enzymatically split off and then released into the blood together with the insulin from the β cells of the pancreas . C-peptide has its own effects on carbohydrate metabolism and its lack may play a role in the development of diabetic organ damage. The C-peptide is no longer present in drug-administered insulins.

proof

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

indication

The C-peptide serves as a marker (measured value) of the secretion of the β-cells of the pancreas . Their ability to react can be determined as part of a glucose load test.

interpretation

Normal values depending on the laboratory

1.1 - 5.0 µg / l
30 - 60 min after glucose exposure: 4.0 - 8.0 µg / l

lowered values

Type 1 diabetes mellitus , e.g. B. also LADA

Type 2 diabetes mellitus when insulin production fails in the later stages of the disease

increased values

Type 2 diabetes mellitus as a sign of insulin resistance

Insulinoma

normal values with clinically proven hypoglycaemia

Hypoglycaemia factitia in the context of Munchausen syndrome .

Relation of C-peptide to fasting blood sugar

In order to determine a diabetic's need for insulin, the ratio of C-peptide to fasting blood sugar (NBC) can be determined. Values below 11.7 indicate secondary failure and the need for insulin administration.

${\ displaystyle {\ frac {C-peptide \ (ng / ml) \ x \ 1000} {NBZ \ (mg / dl)}}}$

Glucose stress test

The glucose load test is used to determine glucose stability. For this purpose, the increase in C-peptide is measured after an intravenous bolus injection of glucose (grape sugar). If there is no or only a slight increase, fluctuations in blood sugar levels are likely despite intensive therapy and good patient cooperation ( compliance ).

Summary

The presence of C-peptides in the blood provides information about the level of the body's own insulin production. The amount of C-peptide is directly proportional to the insulin released. The informative value for diabetes mellitus with slightly reduced values is low. Only the absolute deficiency or significantly reduced values (below 0.5–1.0 µg / l) correlate with symptoms of insulin deficiency requiring substitution. On the other hand, insulin therapy may be necessary due to the insulin resistance even with elevated values . If the value falls below the normal value, insulin therapy can be started, even if only in a low dose, because if insulin is still low, the survival time of the functional β-cells is extended by the early exogenous administration of insulin. In this respect, the level of the C-peptide level has a prognostic value for the course of diabetes mellitus disease.

In insulinoma , the C-peptide plays an important role in diagnosing the disease and can later serve as a tumor marker .

It supports the detection of hypoglycaemia factitia .

Web links

Insulin release - illustration ; Hübl, W .;
Med4You - info page for laboratory diagnostics ; Vienna

swell

literature

Roche Lexicon Medicine [Electronic Resource] 5th edition; Elsevier GmbH, Urban & Fischer Verlag; Munich / Jena 2003; ISBN 3-437-15072-3
Gerd Herold : Internal Medicine . Cologne 2007.
Hellmut Mehnert, Eberhard Standl, Klaus-Henning Usadel, Hans-Ulrich Häring (Eds.): Diabetology in Clinic and Practice 2003 Georg Thieme Verlag ISBN 3-13-512805-9 , also as a limited preview in the Google book search

Individual evidence

↑ Oyer PE, Cho S, Peterson JD, Steiner DF: Studies on human proinsulin. Isolation and amino acid sequence of the human pancreatic C-peptide . In: J. Biol. Chem. . 246, No. 5, March 1971, pp. 1375-86. PMID 5101771 .
Jump up ↑ Hills CE, Brunskill NJ: Cellular and physiological effects of C-peptide . In: Clin. Sci. . 116, No. 7, April 2009, pp. 565-74. doi : 10.1042 / CS20080441 . PMID 19243312 .
↑ Analysis directory laboratory diagnostics. Labor Krone, Bad Salzuflen - medical examination center in the Detmold administrative district; Keyword C-peptide

[1] Oyer PE, Cho S, Peterson JD, Steiner DF: Studies on human proinsulin. Isolation and amino acid sequence of the human pancreatic C-peptide . In: J. Biol. Chem. . 246, No. 5, March 1971, pp. 1375-86. PMID 5101771 .

[2] Jump up ↑ Hills CE, Brunskill NJ: Cellular and physiological effects of C-peptide . In: Clin. Sci. . 116, No. 7, April 2009, pp. 565-74. doi : 10.1042 / CS20080441 . PMID 19243312 .

[3] Analysis directory laboratory diagnostics. Labor Krone, Bad Salzuflen - medical examination center in the Detmold administrative district; Keyword C-peptide