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Category Biochemistry >> Endocrinology
Test background

Pro-insulin is cleaved to form connecting peptide (C-peptide) and insulin prior to secretion into the portal circulation. They are secreted in equi-molar concentrations, however C-peptide is metabolised more slowly than insulin. C-peptide can be helpful in the differential diagnosis of type 1 and 2 diabetes mellitus. The insulin:C-peptide ratio can be used to diagnose use of exogenous insulin.

Clinical Indications

Investigation of hypoglycaemia, where it is a useful aid to differentiate between factitious (exogenous) insulin administration and insulinoma or other forms of endogenous hyperinsulinism. It is useful to monitor pancreatic status (e.g. following pancreatectomy or pancreal/islet cell transplant) and to differentiate between type I type 2 diabetes.

Reference range

See report

Sample & container required SST (gold top) or serum (red top) on ice rush to laboratory
Sample volume 1 mL
Sample collection

Collect into tube on ice, centrifuge and freeze serum immediately.

Transport storage Send to lab frozen.
Turnaround time 1 week

Grossly haemolysed samples are unsuitable for this assay.