Imperial Collage Healthcare

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C-peptide


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

Evaluation of fasting hypoglycaemia: β-cell tumours or factitious causes, eg. abuse of sulphonylureas, exogenous insulin, Classification of diabetes mellitus: in type 1, C-peptide is decreased while, in type 2, C-peptide is normal/raised, Diagnosis of insulinoma, Monitoring purposes (following pancreatectomy or pancreal/islet cell transplant).


Reference Range
C-peptide (pmol/L) ratio to insulin (mIU/L): 30-70


Sample Required
Serum (red top) on ice rush to laboratory


Sample Collection
Collect into tube on ice, separate in a chilled centrifuge and freeze immediately.


Sample Volume
1 mL


Transport/Storage
Send to lab frozen.


Turnaround Time
1 week


Notes
Grossly haemolysed samples are unsuitable for this assay.


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