Definition
What C-Peptide measures
C-peptide is released in equal amounts when the pancreas makes insulin. It lasts longer in the sample than insulin itself, which is why mail-back panels such as SiPhox measure it instead of fasting insulin.
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Glucose & insulinEssentialCompleteng/mL
C-Peptide
A more stable readout of the body's own insulin production
Illustrative sample band · Synthetic
1.8ng/mL
0.3Sample target 0.8–2.5 ng/mL3.7
Why it matters
How clinicians usually read it
It estimates endogenous insulin production from a Tasso+ SST tube. It is not fasting insulin and cannot calculate HOMA-IR. Fasting insulin stays on the venous Complete panel.
When it reads low
A lower value can mean
A lower C-peptide can mean quieter insulin production — or, with a high glucose, that the pancreas is not keeping up. The pair matters more than either value.
When it reads high
A higher value can mean
A higher C-peptide often marks extra insulin demand, similar in direction to insulin resistance. Meals, kidney function, and assay differences still move it.
Questions for a clinician
Bring the number into a real conversation
01
Is this C-peptide high for my HbA1c, suggesting extra demand?
02
Do we still need a venous fasting insulin, or is this enough for now?
03
Could kidney function or a recent meal be lifting this number?
Educational boundary
Educational information only. Displayed ranges are illustrative sample bands, not a diagnosis, treatment plan, or substitute for the contracted laboratory report and a qualified clinician.
See it as a sample result
The sample dashboard shows an illustrative reading, target band, and trend for C-Peptide.