C-peptide and insulin test

Why the Test is Performed

C-peptide is measured to tell the difference between insulin produced by the body and insulin injected into the body. When the pancreas produces insulin, it starts off as a large molecule. This molecule splits into two pieces: insulin and C-peptide. The function of C-peptide is not known.

The C-peptide level may be measured in a patient with type 2 diabetes to see if any insulin is still being produced by the body. It may also be measured in cases of hypoglycemia (low blood sugar) to see if the person's body is producing too much insulin.
 

What Abnormal Results Mean

C-peptide level is based on blood sugar level. C-peptide is a sign that the body is producing insulin. A low level (or no insulin C-peptide) indicates that your pancreas is producing little or no insulin.

http://www.nlm.nih.gov/medlineplus/ency/article/003701.htm

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Why the Test Is Performed

Insulin is a hormone released from the pancreas. Insulin's most important function is to help the cells take up sugar (glucose). Insulin also stimulates the production and storage of triglycerides and proteins.

Insulin is the most important regulator of blood glucose. High blood glucose (such as shortly after a meal) stimulates the release of insulin, whereas low blood glucose levels prevent insulin release.

The most important reason for measuring the blood insulin level is to diagnose or evaluate low blood sugar (hypoglycemia).

Also, insulin levels measured when someone hasn't eaten can give information about the body's sensitivity to insulin. High insulin, even with normal blood sugar, may indicate that the pancreas is working harder than normal to lower the blood-sugar level. This situation is usually caused by the body being resistant to insulin's effect -- a condition called "insulin resistance syndrome." It is very common with obesity, and hormonal problems such as polycystic ovary syndrome.

The insulin test may also be combined with other tests, such as:

• Anti-insulin antibodies
• Glucose
• Insulin C-peptide
• Proinsulin

Normal Results

Normal values are are 5-20 mcU/mL while fasting. (Note: mcU/mL = micro unit per milliliter)

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

What Abnormal Results Mean

Greater than normal levels may indicate:

• Injection of too much insulin
• Insulinoma
• Type 2 diabetes mellitus
• Obesity
• Sulfonylurea-induced hypoglycemia

Lower than normal levels may indicate:

• Diabetes, type 1 or 2