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C-peptide -What does it tell about your Diabetes?

What is C-peptide?

Let us see what is C-peptide? C-peptide or connecting peptide is also known as Proinsulin C-peptide. It consists of 31 amino acids and is the middle segment of proinsulin in between the two chains. When proinsulin undergoes cleavage, insulin and C-peptide are released. Since equal amounts of insulin and C-peptide are produced, C-peptide is used as a marker of endogenous insulin secretion and the condition of insulin producing pancreatic beta cells which regulate the blood sugar levels, hence playing a major role in Diabetes.

C-peptide levels are increased in insulinoma (tumor of pancreatic cells), insulin resistance state such as obesity, chronic kidney disease and during consumption of medications for Diabetes such as sulfonylureas. It is decreased in Type 1 Diabetes mellitus, exogeneous insulin injection (factitious) and insulin independent hypoglycemia.

Pay attention to some points while C-peptide testing

  • Your doctor will order a C-peptide test along with a blood glucose test.
  • If you have Type 2 Diabetes, then you often have a normal or high level of C-peptide in the blood. With time, you may develop a low level of C-peptide.
  • Most doctors consider a person's age, weight, and how long symptoms have been present to assist in differentiation between Type 1 and Type 2 Diabetes. A C-peptide stimulation test may be done to know the difference between the two types of Diabetes. During a C-peptide stimulation test, a blood sample is taken to measure C-peptide. Then a shot of a hormone to increase blood sugar is given into a vein in the arm and another blood sample is taken. If you have Type 1 Diabetes, your C-peptide levels will be low since the pancreas cannot make any insulin in response to the glucagon. If you have Type 2 Diabetes, C-peptide levels will be higher than the first blood test since more insulin is made by pancreas in response to the glucagon.

Indications of C-peptide testing

It is essential for you to know when your doctor will order C-peptide testing. The indications for C-peptide testing include: differentiating Type 1 and Type 2 diabetes, assessing the cause of hypoglycemia, assessing treatment response in Diabetes patients and determining prognosis and transplant options.

You might want to gain further understanding of the conditions and their relation with C-peptide to have an insight about your Diabetes. We will discuss these conditions briefly here:

Differentiating Type 1 and Type 2 Diabetes - C-peptide test determines if you have Type 1 or Type 2 Diabetes. In Type 1 Diabetes, your pancreas does not make any insulin and has a low level of insulin and C-peptide. There is a rapid decline in the insulin/ C-peptide levels from the time of initial diagnosis. The majority of patients have low C-peptide levels between 3-5 years of the diagnosis, when usefulness of this test increases. If you have Type 2 Diabetes, then you have adequate levels of insulin produced by the pancreas but the cells cannot utilize it as well as they should and you can have a normal or high level of C-peptide.

Assessing the cause of hypoglycemia - You may have low blood sugar or hypoglycemia due to increased use of medicine to treat diabetes or a noncancerous growth or tumor in the pancreas known as insulinoma. C-peptide test can assess and find the cause of hypoglycemia. If you have a low blood sugar level from taking too much insulin, you will have a low C-peptide level but a high level of insulin since man-made or synthetic insulin does not have C-peptide. In insulinoma, the pancreas releases excess insulin, which leads to falling of blood sugar levels or hypoglycemia. Hence, in an insulinoma you will have a high level of C-peptide in the blood in presence of a high level of insulin.

Assessing treatment response in Diabetes patients -  If you have been treated with insulin and have sufficient pancreatic cell function, you may get your insulin replaced with hypoglycemia therapies depending on C-peptide levels. Thus, insulin requiring diabetes can be differentiated from non-insulin requiring diabetes.  C-peptide measurement can also assess if you are an adult patient presenting with diabetic ketoacidosis and do not have classical Type 1 diabetes findings such as presence of pancreatic autoantibodies. C-peptide levels are within normal range in such cases. Likewise, in Type 2 diabetes C-peptide testing may lead to a clinical decision by your doctor for initial insulin therapy.

Determining prognosis and requirement of transplant - In Type 1 Diabetes, C-peptide levels can detect your even highly modest pancreatic function which is linked to improved glycemic control, less fall in blood sugar levels and decrease in further complications. Your high C-peptide levels in Type 2 Diabetes are usually associated with metabolic syndrome and increased complications. Further, C-peptide test can be used to help selecting patients for pancreatic cell transplantation and post-transplant monitoring, according to the set criterion.

Your doctor will determine your Diabetes type, treatment options and prognosis based on your blood tests, history and physical assessment. C-peptide test facilitates the process of diagnosis and decision making for your doctor and makes your life manageable.