C-peptide

What it measures

C-peptide is released in equal amounts with insulin when proinsulin is split. It reflects the body's own insulin production and helps distinguish type 1 from type 2 diabetes and investigate hypoglycaemia.

Specimen and preparation

• Specimen: Serum or lithium-heparin plasma
• Tube: Gold top
• Preparation: Fasting sample, or timed with glucose; separate and freeze promptly.

Reference range

Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.

Causes of high values

• Insulinoma
• Sulfonylurea use
• Type 2 diabetes with insulin resistance
• Kidney failure (reduced clearance)

Causes of low values

• Type 1 diabetes
• Exogenous insulin injection (factitious hypoglycaemia)
• Pancreatectomy
• Long-standing type 2 diabetes

Method

Chemiluminescent immunoassay

Good to know

High insulin with low C-peptide during hypoglycaemia indicates injected insulin.

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