C-peptide is used to monitor insulin production and kidney function. The test is not used to diagnose diabetes. Instead, it is used to determine how much insulin a person's pancreas is still producing.
Sometimes a C-peptide test may be used to help evaluate a person diagnosed with metabolic syndrome - a set of risk factors that includes abdominal obesity, insulin resistance, dyslipidemia, and hypertension.
High levels of C-peptide generally indicate increased production of insulin. This may be in response to high levels of blood glucose and/or insulin resistance. High levels of C-peptide are also seen with pregnancy, Cushing's syndrome, and kidney dysfunction.
Low levels are commonly associated with insulin treatment since C-peptide concentrations reflect only the body’s own production of insulin and not administered insulin (such as in an insulin dependent diabetic). It provides information about how much insulin the islet cells in the pancreas are still able to produce. Combining C-peptide with other tests such as glucose and insulin can help provide more information to support appropriate management and therapy of those with glucose management issues and especially for those who are taking insulin.
A 14 to 16 hour fast is required for this blood test. However, drink plenty of water and take your medications as prescribed.