What It Is
C-peptide, like the hormone insulin, is produced in the pancreas. Both are released
simultaneously from the pancreas when the compound called proinsulin is split into
two pieces.
Insulin is responsible for regulating the body's glucose levels. Glucose, the body's
main source of energy, is a sugar that comes from foods.
After a meal, our bodies break down the foods we eat into glucose and other nutrients,
which are then absorbed into the bloodstream from the gastrointestinal tract. Glucose
levels in the blood rise after a meal and trigger the pancreas to make insulin and
release it into the blood. When insulin is released, so is C-peptide.
Insulin works like a key that opens the doors to cells and allows the glucose in.
Without insulin, glucose can't get into the cells and it stays in the bloodstream.
The most common cause of abnormal fluctuations in blood glucose is diabetes.
C-peptide, on the other hand, has no effect on blood sugar. It is, however, useful
as a marker of insulin production, since the pancreas typically releases C-peptide
and insulin in about equal amounts.
In general, high C-peptide levels are associated with increased insulin production,
while low C-peptide levels indicate decreased insulin production.
Why It's Done
The C-peptide test may be ordered to determine how much insulin is being made by
the pancreas. This information is useful because:
- It can help doctors tell the difference between type 1 and type 2 diabetes. In
type 1 diabetes, the pancreas produces little or no insulin and little or no C-peptide.
In type 2 diabetes, C-peptide levels will typically be normal or high, as the pancreas
works harder to overcome insulin resistance (when the tissues become less sensitive
to the effects of insulin) by producing more insulin.
- It can help find the cause of low blood sugar (hypoglycemia), including the incorrect
use of diabetes medications.
Preparation
Your doctor will let you know if any special preparations are needed for this test.
Sometimes it's necessary for a child to avoid eating or drinking for 8 hours prior
to the test; in other cases, doctors may want to check levels at specific times, such
as timed intervals after food or glucose is given.
On the day of the test, having your child wear a T-shirt or short-sleeved shirt
can make things easier for your child and the technician who will be drawing the blood.
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