Patient should fast 12 hours prior to collection
is useful in the evaluation of pancreatic beta cell function (e.g.,
helping distinguish type 1 from type 2 diabetes mellitus, or monitoring
patients who have received islet cell or pancreatic transplants) and for
determining the source of insulin in patients with hyperinsulinemic
hypoglycemia (e.g., distinguishing insulin-secreting tumors from
exogenous insulin administration). It is also sometimes measured as an
additional means (more resistant to hemolysis than is insulin itself)
for evaluating glucose tolerance tests.
How is it used?
C-peptide testing can be used for a few different purposes. C-peptide is a substance produced by the in the pancreas when proinsulin splits apart and forms one molecule of C-peptide and one molecule of insulin. Insulin is the that is vital for the body to use its main energy source, glucose. Since C-peptide and insulin are produced at the same rate, C-peptide is a useful marker of insulin production.
The following are some purposes of C-peptide testing:
- A C-peptide test is not ordered to help diagnose diabetes, but when a person has been newly diagnosed with diabetes, it may be ordered by itself or along with an insulin level to help determine how much insulin a person's pancreas is still producing ( insulin).
- In type 2 diabetes, the body is resistant to the effects of insulin (insulin resistance)
and it compensates by producing and releasing more insulin, which can
also lead to beta cell damage. Type 2 diabetics usually are treated with
oral drugs to stimulate their body to make more insulin and/or to cause
their cells to be more sensitive to the insulin that is already being
made. Eventually, because of the beta cell damage, type 2 diabetics may
make very little insulin and require injections. Any insulin that the
body does make will be reflected in the C-peptide level; therefore, the
C-peptide test can be used to monitor beta cell activity and capability
over time and to help a health practitioner determine when to begin
- People who are on insulin therapy, regardless of the source of the insulin, may develop
to insulin. These typically interfere with tests for insulin, making
it nearly impossible to directly evaluate endogenous insulin production.
In these cases, C-peptide measurement is a useful alternative to
testing for insulin.
- C-peptide measurements can also be used in conjunction with insulin and glucose levels to help diagnose the cause of documented
and to monitor its treatment. Symptoms of hypoglycemia may be caused
by excessive supplementation of insulin, alcohol consumption, inherited
liver enzyme deficiencies, liver or kidney disease, or by .
- The C-peptide test may be used to help diagnose Insulinomas. These are tumors of the in the pancreas that can produce uncontrolled amounts of insulin and C-peptide and can cause
episodes of hypoglycemia. C-peptide tests may be used to monitor the
effectiveness of insulinoma treatment and to detect recurrence.
- Sometimes a C-peptide test may be used to help evaluate a person diagnosed with metabolic syndrome,
a set of risk factors that includes abdominal obesity, increased blood
glucose and/or insulin resistance, unhealthy blood lipid levels, and
high blood pressure (hypertension).
- Rarely, when someone has had his pancreas removed or has had
pancreas islet cell transplants, intended to restore the ability to make
insulin, C-peptide levels may be used to verify the effectiveness of
treatment and continued success of the procedure.
When is it ordered?
C-peptide levels may be ordered when a person has been newly diagnosed with type 1 diabetes as part of an evaluation of the person's "residual function."
With type 2 diabetes,
the test may be ordered on a regular basis when a health practitioner
wants to monitor the status of a person's beta cells and insulin production over time and to determine if/when insulin injections may be required.
C-peptide levels may be done when there is documented or recurring low blood glucose () and/or excess insulin is suspected. Symptoms of hypoglycemia include:
- Blurred vision
- In severe cases, seizures and loss of consciousness
However, many of these symptoms can occur with other conditions as well.
When a person has been diagnosed with an , a C-peptide test may be ordered periodically to monitor the effectiveness of treatment and to detect tumor recurrence.
Rarely, C-peptide levels may be monitored over time when someone has had his pancreas removed or has had pancreas transplants.
What does the test result mean?
A high level of C-peptide generally indicates a high level of insulin production. This may be in response to a high blood glucose caused by glucose intake and/or insulin resistance. A high level of C-peptide is also seen with and may be seen with low blood potassium, Cushing syndrome, and renal failure.
When used for monitoring, decreasing levels of C-peptide in someone
with an insulinoma indicate a response to treatment; levels that are
increasing may indicate a tumor recurrence.
A low level of C-peptide is associated with a low level of insulin
production. This can occur when insufficient insulin is being produced
by the , with diabetes for example, or when production is suppressed by treatment with insulin.
Is there anything else I should know?
C-peptide testing is
not widely used and may not be available in every laboratory. If a
series of C-peptide tests are going to be performed, they should be done
at the same laboratory using the same method.
Even though they are produced at the same rate, C-peptide and insulin
leave the body by different routes. Insulin is processed and eliminated
mostly by the liver, while C-peptide is removed by the kidneys. Since
of C-peptide is about 30 minutes compared to insulin's 5 minutes,
normally there will be about 5 times as much C-peptide in the blood as