Nearly each of us knows someone who has diabetes. Being diagnosed with diabetes for the first time can be a tricky affair and there is usually a battery of tests conducted to confirm it. Along with the routine fasting and post lunch blood sugar levels, your doctor might order a C- peptide blood test as well.
C-peptide is a protein consisting of 31 amino acids. It is produced by the same cells of your pancreas that secrete insulin and hence is found in equal amounts as that of insulin. Insulin is the hormone that helps in regulating blood sugar levels. Insulin permits the entry of glucose into the body cells where it is used for energy. C-peptide does not affect the blood sugar levels in the body. Most of the C-peptide is excreted by the kidney and it remains in the body 3-4 times longer than insulin.
How does C-peptide test help in diagnosing diabetes?
A C-peptide test will measure the level of this peptide in your blood sample. Since both insulin and C-peptide are produced at the same time, the level of C-peptide in your blood can show how much insulin is being made by your pancreas.
This test is done when someone is just diagnosed for having diabetes and it is not yet clear whether it is type 1 or type 2 diabetes. If the person is suffering from type 1 diabetes, (which means no insulin is being made by the pancreas) the C-peptide levels would be very low. If the person is suffering from type 2 diabetes he may have normal or high level of C-peptide.
Occasionally, there is a condition when a person has very low blood sugar (hypoglycemia) and high insulin levels in blood, but the exact cause of this is to be analyzed. There are two possibilities. Either the person has injected too much of insulin or his pancreas is secreting too much insulin (possibly due to insulinoma: a non-cancerous tumor of pancreas). This test can also be used as a tool to resolve this problem. As synthetic insulin is man-made, the amount of C-peptide for it in blood will not be the same. Hence in case 1, there will be a low C-peptide level. But in case 2, i.e. if there is increased release of insulin from pancreas, the person will have a high level of both C-peptide and insulin in their blood sample.
The test is useful even after surgical removal of such an insulinoma. If the C-peptide levels are high even after the surgery, it can suggest that the tumor has returned or that the tumor has metastasized.
Furthermore if you are suffering from any liver disease, a severe infection, or Addison’s disease, the levels of both your C-peptide and blood glucose will be low.
Thus, C-peptide level is a very useful tool in treatment and management diabetes, despite the fact that it has no effect on blood glucose levels.