A C-peptide test measures the level of this
peptide in the blood. It is generally found in amounts equal to
insulin because insulin and C-peptide are linked when first made by the
pancreas. Insulin helps the body use and control the amount of sugar (glucose)
in the blood. Insulin allows glucose to enter body cells where it is used for
energy. The level of C-peptide in the blood can show how much insulin is being
made by the
pancreas. C-peptide does not affect the blood sugar
level in the body. See a picture of the
A C-peptide test can be done
diabetes has just been found and it is not clear
type 1 diabetes or
type 2 diabetes is present. A person whose pancreas
does not make any insulin (type 1 diabetes) has a low level of insulin and
C-peptide. A person with type 2 diabetes can have a normal or high level of
A C-peptide test can also help find the cause of low
blood sugar (hypoglycemia), such as excessive use of medicine to
treat diabetes or a noncancerous growth (tumor) in the pancreas (insulinoma).
Because man-made (synthetic) insulin does not have C-peptide, a person with a
low blood sugar level from taking too much insulin will have a low C-peptide
level but a high level of insulin. An insulinoma causes the pancreas to release too much insulin, which
causes blood sugar levels to drop (hypoglycemia). A person with an insulinoma
will have a high level of C-peptide in the blood when they have a high level of insulin.
E. Gregory Thompson, MD - Internal Medicine
Alan C. Dalkin, MD - Endocrinology
June 20, 2012
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