A health professional uses a needle to take a blood sample, usually from the arm.

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When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.

There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.

Normal

Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.

High values

• High levels of both C-peptide and blood glucose are found in people with type 2 diabetes or insulin resistance (such as from Cushing's syndrome).
• A high level of C-peptide with a low blood glucose level may mean that an insulin-producing tumour of the pancreas (insulinoma) is present. Or it may mean that the use of certain medicines such as sulfonylureas (for example, glyburide) is causing the high level.
• If C-peptide levels are high after an insulinoma is taken out, it may mean that the tumour has returned or that the tumour has spread to other parts of the body (metastasized).

Low values

• Low levels of both C-peptide and blood glucose are found in liver disease, a severe infection, Addison's disease, or insulin therapy.
• A low level of C-peptide with a high blood glucose level is found in people with type 1 diabetes.
• Complete removal of the pancreas (pancreatectomy) causes a C-peptide level so low it can't be measured. The blood glucose level will be high, and insulin will be needed in order for the person to survive.