Peptide fragment analysis of proinsulin (specifically the C-peptide portion) via immunoassay

Why Is This Test Done?

Your doctor may order a C-peptide test to check if your pancreas is producing insulin properly. It’s often used to diagnose or monitor type 1 or type 2 diabetes, especially when insulin levels alone aren’t enough to explain symptoms. It can also help distinguish between insulin-dependent diabetes (type 1) and insulin-producing diabetes (type 2).

How Is the Test Performed?

A blood sample is taken from a vein in your arm. The sample is sent to a lab, where it’s analyzed using an immunoassay method to detect the presence of C-peptide. No special preparation is usually needed, but you may be asked to fast for a few hours before the test.

What Does the Test Result Mean?

A low or absent C-peptide level often suggests type 1 diabetes, where the pancreas doesn’t produce insulin at all. In type 2 diabetes, C-peptide levels may be normal or slightly reduced, indicating some insulin production remains. Very high levels could indicate overproduction of insulin, which may require further evaluation.

Common Reasons for Testing

Doctors may recommend this test if you have unexplained symptoms of diabetes, such as frequent urination, extreme thirst, or unexplained weight loss. It’s also used in research or clinical settings to assess insulin secretion in people with suspected pancreatic disorders or those undergoing diabetes treatment.