Insulin C-Peptide Test

Written by Ann Pietrangelo | Published on October 3, 2012
Medically Reviewed by Peggy Pletcher, MS, RD, LD, CDE on May 29, 2014

What Is an Insulin C-Peptide Test?

Insulin is the hormone that is primarily responsible for lowering glucose (sugar) levels in the blood. It is produced by beta cells (specialized cells in the pancreas). When we eat, our bodies begin to break food down into glucose and other nutrients.

In response to this, the pancreas produces insulin, which allows cells to absorb glucose from the blood. C-peptide is byproduct created when insulin is produced. Because of this, measuring the amount of C-peptide in blood indicates how much insulin is being produced. Generally, high C-peptide production indicates high insulin production, and vice versa.

Who Benefits from an Insulin C-Peptide Test?

The insulin C-peptide test (or simply the C-peptide test) is used to monitor insulin production in the body and determine the cause of hypoglycemia (low blood sugar). The test is often ordered when someone is newly diagnosed with type 1 diabetes, to reveal how much insulin the pancreas is producing. It is also sometimes used to distinguish between type 1 and type 2 diabetes if the doctor is not sure which type of diabetes is present. It can also provide information about how well the beta cells in the pancreas are working.

The test may also be performed for patients who experience symptoms related to hypoglycemia in the absence of type 1 or type 2 diabetes. In this case, the body may be producing too much insulin. Symptoms of hypoglycemia include:

  • sweating
  • heart palpitations
  • excessive hunger
  • nervousness or irritability
  • confusion
  • blurred vision
  • fainting
  • seizures and/or loss of consciousness

How Does a Patient Prepare for an Insulin C-Peptide Test?

The preparation needed for the insulin C-peptide test depends on a person’s age and the reason for the test. In some instances, you may be required to fast for up to 12 hours before the test. Fasting requires that you to not eat or drink anything but water before the test. You may also need to stop taking certain medications. Your doctor will provide you with specific instructions based on your particular medical needs.

How Is an Insulin C-Peptide Test Administered?

The insulin C-peptide test requires a blood sample administered by a qualified doctor or nurse. The blood is drawn from a vein, typically in the arm or from the back of your hand. The procedure can cause minor discomfort, but it will be temporary. The blood will be collected in a tube and sent to a lab for analysis.

Results are typically available within a few days. Your doctor will be able to provide you with more information about the results and what they mean. In general, normal results for C-peptide in the bloodstream are between 0.5 and 2.0 ng/mL (nanograms per milliliter). However, results for the insulin C-peptide test may vary based on the lab.

What Are the Risks of an Insulin C-Peptide Test?

The insulin C-peptide test may cause some discomfort when the blood sample is drawn. Common side effects include temporary pain or throbbing at the injection site. Less common side effects include:

  • difficulty obtaining a sample, resulting in multiple needle sticks
  • excessive bleeding at the needle site
  • fainting as a result of blood loss
  • the accumulation of blood under the skin, known as a hematoma (bruise)
  • infection where the skin is broken by the needle
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