Insulin and C-Peptide
المؤلف:
Marcello Ciaccio
المصدر:
Clinical and Laboratory Medicine Textbook 2021
الجزء والصفحة:
p409
2025-11-08
55
Routine testing of insulin and C-peptide is not recommended in most patients with diabetes. However, the assay of these analytes is indicated in the evaluation of fasting hypoglycemia to exclude the presence of an insulinoma. The diagnosis of insulinoma is based on the persistence of an elevated plasma insulin concentration associated with a decreased glucose concentration. Insulin determination is also helpful in evaluating and managing patients with polycystic ovary syndrome.
C-Peptide is a fragment of the original molecule from which insulin is formed. When endogenous insulin is produced, C-peptide is also released. In patients undergoing insulin therapy, to verify the secretory capacity of β cells, it is not possible to directly evaluate insulinemia because the insulin administered as a drug would also be measured. In these cases, it is indicated to evaluate the concentration of C-peptide (which is not contained in the pharmacological insulin) to verify the residual capacity of β-cells to produce endogenous insulin.
Measurement of the C-peptide response to glucagon may help in rare cases where it is difficult to differentiate the diagnosis between type 1 and type 2 diabetes..
The determination of C-peptide is essential in evaluating possible self-induced hypoglycemia due to nontherapeutic insulin intake.
Analytical Aspects
Immunometric methods can measure insulin and C-peptide, but despite the efforts of the scientific community, to date, there are no standardized methods.
One of the analytical problems affecting these analytes’ measurements is cross-reactivity with insulin analogs.
Postanalytical Aspects
Insulin reference ranges depend on the method used and must therefore be defined by each laboratory. After an overnight fast, the insulin concentration in a healthy, nonobese subject is usually between 12 and 150 pmol/L. For C-peptide, reference ranges have not been defined with certainty, and different laboratories express C- peptide values with different units (nmol/L, pmol/L, or ng/mL). The concentration of C-peptide in the healthy population is usually between 0.78 and 1.89 ng/mL (0.25–0.6 nnmol/L).
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