C-peptide is a byproduct of insulin production, usually
by the pancreas. The level of C-peptide is a gauge of how much insulin is being
produced in the body. C-peptide is made up of chemical compounds called amino
acids. When the pancreas produces insulin, it releases C-peptide into the bloodstream
at the same time. The amount of C-peptide in the blood can indicate the presence
or absence of disease. For example, abnormally low amounts of C-peptide in the
blood suggest the insulin production is too low (or absent) because of type
I diabetes, also known as juvenile or insulin- dependent diabetes.
Abnormally high amounts of C-peptide warn of the possible presence of a tumor
called an insulinoma that secretes insulin. Normal levels of C-peptide
may signal that all is well. However, in a person with diabetes, a normal level
of C-peptide indicates the body is making plenty of insulin but the body is
just not responding properly to it. This is the hallmark of type 2 diabetes
(adult onset insulin-resistant diabetes). This slides into the metabolic syndrome (aka syndrome-X) when the pancreas produces too much insulin producing a state of insulin toxicity.