METABOLIC
C-Peptide
Also known as C-Pep
What it is
C-peptide is a fragment cleaved from proinsulin whenever the pancreas releases insulin. It circulates longer than insulin, so it gives a stable picture of how much insulin the body is actually producing.
Why it matters
C-peptide is the cleanest measure of endogenous insulin production. Unlike fasting insulin, it is not affected by exogenous insulin. It refines the metabolic picture in patients with insulin resistance, type 2 diabetes, or on GLP-1 therapy — and is one of the few tests that distinguishes type 1 from advanced type 2 diabetes.
Range GPLX watches for
GPLX watches for C-peptide values within the lab reference range in metabolically healthy patients. Elevated C-peptide with normal glucose suggests early insulin resistance; low C-peptide with elevated glucose raises concern for beta-cell failure.
This educational range is not a personal diagnostic threshold. Your physician interprets your result in context of your full biomarker panel, medications, symptoms, and history.
What abnormal values can suggest
If low
A low C-peptide value can suggest type 1 diabetes, late-stage type 2 diabetes with beta-cell exhaustion, or pancreatic disease.
If high
A high C-peptide value can suggest insulin resistance, early type 2 diabetes, obesity, or, rarely, an insulinoma.
This marker is reviewed when clinically appropriate as part of physician-directed labs. Membership is $39.99/month; consultation is $30.
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