Insulin C-peptide test

Insulin C-peptide is a laboratory test that measures the level of C-peptide amount in the blood. C-peptide is a part of proinsulin that is produced by pancreas. Insulin is a hormone that is produced when the blood sugar level increases and it is related with glucose transport to the body cells and energy production in them.  C-peptide is a break down product from the proinsulin, it connects the A and B chains of proinsulin and its name comes from “connecting peptide”. C-peptide is found in blood circulation as a seperated part and provides information about pancreas functions. If insulin production is in normal range C-peptide level will be normal too. Blood C-peptide level is an indicator of insulin production by pancreas.

C-peptide production in the body

C-peptide occurs during the insulin production by pancreas beta cells. It is excreted with the insulin to the blood circulation. C-peptide level increases or decreases according to insulin production level.

How the C-peptide test is done?

A blood sample is needed for this test. Your nurse or technician will insert a needle  (usually) into your arm vein and collect a tube of blood. All process takes 1-2 minutes, you may feel a little pain during the blood collection for a few seconds.

Preparation for C-peptide test

Your doctor may recommend you to fast for 8-10 hours before the test. Some medicines may affect your test result so please inform your doctor about the medicinies you use regularly. Follow your doctor’s and laboratory technician’s instructions before the test.

Factors that may affect C-peptide test result

  • Kidney failure
  • Obesity
  • Insuline usage; type-2 diabates medicine
  • Sulfonylurea usage; type-2 diabetes medicine

Why the C-peptide test is done?

  • Determining the type of diabetes if it is type-1 or type-2. In type-1 diabetes insulin production by pancreas is very low and according to this C-peptide level is found very low too. In type-2 diabetes C-peptide level may be found normal or high.
  • Determining the cause of hypoglycemia; pancreas tumor insulinoma may cause so much insulin secretion and so hypoglycemia. In this case insulin and C-peptide levels both increases. If insulin is taken by injection , insulin level will found higher but C-peptide level will be low
  • Evaluating the person’s residual beta cell function
  • Determining the success of insulinoma tumor if it is removed completely or not

C-peptide test normal levels

These values may change according to the laboratory, test method and the analyser

Blood C-peptide normal level: 0.51-2.72 ng/mLc-peptid

High C-peptide result causes

  • Type-2 diabetes
  • Insulin resistance
  • Insulinoma
  • Recurrence of insulinoma after surgery

Low C-peptide result causes

  • Type-1 diabetes
  • Liver diseases
  • Severe infections
  • Addison disease
  • Insulin treatment


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