How to Read C-peptide Test Report

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C-peptide Test:

C-peptide test is carried out to measure the levels of C-peptide in blood. C-peptide is a widely used measure of pancreatic beta cell function. C-peptide is released by pancreas alongside insulin. Estimation of C-peptide levels can help determine the amount of insulin produced by the body. The test helps in determining the cause of hypoglycemia and distinguish between type 1 and type 2 diabetes. The test is also known as Insulin C-peptide test.

Factors involved to understand the normal range of C-peptide levels:

  1. What is the normal range of C-peptide?
  2. What do high levels of C-peptide mean?
  3. Causes of high C-peptide levels
  4. What do low levels of C-peptide mean?
  5. Causes of low C-peptide levels
  6. Are there any risks associated with C-peptide test?
  7. What other tests are ordered along with C-peptide test?

What is the normal range of C-peptide?

The normal range of C-peptide in blood is between 0.5 to 2.0 ng/mL. In healthy individuals, the plasma concentration of C-peptide in the fasting state is 0.3–0.6 nmol/l, with a postprandial increase to 1–3 nmol/l.

What do high levels of C-peptide mean?

A high level of C-peptide can point to several conditions. It generally indicates a high level of insulin present in the body. It can be an indication of disorders such as:

  • Type 2 diabetes
  • Insulin resistance
  • Cushing’s syndrome
  • Insulinoma (a tumor of the pancreas)
  • Kidney disease
  • Hyperthyroidism
  • Cirrhosis

Certain medications that treat type 2 diabetes can also cause high levels of C-peptide. C-peptide levels also increase with weight and age in healthy, non-diabetic people.

Causes of high C-peptide levels

High levels of C-peptide indicate high levels of insulin. This can be due to excessive production of insulin by the body in response to the high levels of glucose generally caused by increased glucose intake or insulin resistance. Insulin resistance occurs when the cells do not respond normally to the insulin already present, and hence, the pancreas secrete more insulin to compensate.

High levels of C-peptide are also due to insulinomas, a rare tumor of the pancreas that leads to an excessive insulin production. Other conditions such as hypokalemia, pregnancy, Cushing’s syndrome, and kidney diseases also elevate C-peptide levels. Certain diabetes drugs called sulfonylureas also raise levels of C-peptide.

Obesity is also one the factors that causes an increase in C-peptide levels.

What do low levels of C-peptide mean?

Low levels of C-peptide in the blood indicates that the body is not producing enough insulin. It also indicates inefficient functioning of pancreas. Low levels are also an indication of conditions such as:

  • Type 1 or type 2 diabetes
  • Suppression of insulin release because of insulin shots
  • Hypoglycemia
  • Shrinkage of insulinoma due to treatment

Low levels can also mean the ongoing treatment for diabetes is not efficient.

Causes of low C-peptide levels

Low C-peptide levels indicate low levels of insulin. C-peptide levels get low in both type 1 and type 2 diabetes. However, people with type 1 diabetes have a significantly lower level of C-peptide as compared to type 2 diabetics.

Low levels are also seen when there is insufficient production of insulin by the pancreas. Injected insulin results in suppression of the insulin production, thereby decreasing the levels of C-peptide and insulin. Other factors that lower the levels of C-peptide include diuretics and alcohol.

C-peptide and blood glucose levels both decrease in severe liver disease, severe infection, Addison’s disease, and insulin therapy. Complete removal of pancreas also results in extremely low and immeasurable levels of C-peptide. In such cases, exogenous insulin is required to control blood glucose levels.

Are there any risks associated with C-peptide test?

A blood sample test can possess certain risks such as bruising, bleeding, or infection at the site of puncture. Patients can also experience dizziness or fainting at the sight of blood. A slight stinging sensation and pain may be experienced during the sample collection. However, these side effects do not require treatments and generally resolve on their own.

What other tests are ordered along with C-peptide test?

C-peptide test provides comprehensive information about the type of diabetes a person has and whether diabetes treatment is working. However, the test cannot be used to diagnose diabetes and hence, other tests are often ordered along with C-peptide test to confirm the diagnosis of diabetes.

Tests such as blood glucose test, glucagon test, HbA1c test, and insulin assay are ordered along with this test to confirm the cause of high or low sugar and C-peptide levels. Urine glucose analysis is also ordered to screen and diagnose diabetes.

Various methods of sampling are available, including a urinary C-peptide to creatinine ratio, fasting serum C-peptide, and stimulated C-peptide. Comparing in sensitivity and convenience of the test, glucagon stimulation testing is usually recommended in clinical practice.

Certain precautions are required to be taken before undergoing this test. Patient may need to fast for 8-12 hours before the blood test. If a urine test has been ordered, ask your healthcare provider about any specific instructions that you may need to follow.

It is important to provide complete information to your health care provider about all medicines, herbs, vitamin supplements, over-the-counter-medications, or drugs that you may be taking. These factors can affect the C-peptide levels and give wrong results on the test.


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