C-Peptide
Also written as: Connecting Peptide, Insulin C-Peptide
A by-product of insulin production, used to gauge how much insulin the pancreas makes.
What it measures
The concentration of C-peptide, a fragment released into the blood in equal amounts with every molecule of insulin the pancreas makes. It reflects the body's own insulin production, and unlike insulin itself it is absent from injected insulin.
Why a doctor orders it
Ordered to gauge how much insulin the pancreas is producing on its own. Common situations include telling forms of diabetes apart, evaluating episodes of low blood sugar, and separating the body's insulin from injected insulin.
What is generally associated with a higher result
Broadly associated with increased insulin production, as seen with insulin resistance and, rarely, with insulin producing tumors. Also linked with reduced kidney function, because the kidneys clear C-peptide from the blood.
What is generally associated with a lower result
Broadly associated with reduced insulin production by the pancreas. Prolonged fasting before the draw also lowers it.
Everyday things that move this number
Not every shift in a value reflects disease. These are ordinary factors known to affect this particular measurement:
- Whether the sample was fasting or after food, which changes it substantially
- Kidney function, which affects how quickly it is cleared
- Sample handling and delays before processing
- Steroid medicines and other drugs that shift insulin output
Questions to take to your appointment
- Was this a fasting or a stimulated measurement, and how does that change what it shows?
- Should my kidney function be considered when reading this value?
- Was a glucose level drawn at the same moment?
Build a printable questionnaire with your own results →
Where to read more
MedlinePlus, from the US National Library of Medicine, publishes patient-facing pages on individual lab tests and is a reliable next stop: medlineplus.gov/lab-tests .
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