To monitor insulin production by the beta cells in the pancreas and to help determine the cause of hypoglycaemia (low blood sugar) or assessment of insulin resistance (which can help diagnose the type of diabetes mellitus a person has or the severity of the metabolic syndrome).
C-peptide
If you have diabetes mellitus and your doctor wants to see if you are producing any of your own insulin, if you are thought to be insulin resistant (when your body does not respond properly to insulin), or to help establish if it is time to add insulin injections to your current treatment. Your doctor also may request a C-peptide blood test if you have an episode of low blood sugar, called hypoglycaemia.
A blood sample taken from a vein in your arm and sometimes a 24-hour urine sample is taken, or urine sample 2 hours after your largest meal of the day is taken.
Fasting for 8 to 10 hours before blood testing may be required, alternatively a meal stimulus or symptoms present thought to be due to hypoglycaemia.