Insulin is a peptide hormone secreted by pancreatic beta cells that regulates glucose homeostasis by facilitating cellular glucose uptake and suppressing hepatic glucose production. C-peptide is the connecting peptide cleaved from proinsulin during insulin biosynthesis and is co-secreted in equimolar amounts with insulin, serving as a reliable endogenous marker of beta-cell secretory function. Because C-peptide has a longer half-life and is not cleared by the liver, it provides a more stable and accurate reflection of insulin secretion than insulin itself. Proinsulin is synthesized in pancreatic beta cells and cleaved into equimolar quantities of insulin and C-peptide before secretion into the portal circulation. Insulin binds to insulin receptors on target tissues—primarily liver, skeletal muscle, and adipose—to promote glucose uptake, glycogen synthesis, lipogenesis, and protein anabolism while inhibiting gluconeogenesis and lipolysis. C-peptide undergoes minimal hepatic extraction and is cleared primarily by the kidneys, making it a more consistent surrogate for beta-cell insulin output, particularly in patients receiving exogenous insulin therapy.
Insulin is a hormone made by your pancreas that helps your body use sugar for energy. C-peptide is a small protein released at the same time as insulin and can be measured to show how much insulin your own body is making—even if you are taking insulin injections. Together, these two tests help doctors understand how well your pancreas is working, whether your body is responding properly to insulin, and whether low blood sugar episodes are caused by your own insulin or from another source. Abnormal results do not by themselves diagnose a condition; your doctor will interpret them alongside your symptoms, medical history, and other test results.
When elevated: Elevated fasting insulin and C-peptide may indicate insulin resistance, metabolic syndrome, early type 2 diabetes, polycystic ovary syndrome, obesity, or endogenous hyperinsulinism such as insulinoma or nesidioblastosis. Disproportionately high insulin relative to C-peptide raises concern for exogenous insulin administration. When low: Low or undetectable C-peptide suggests significant beta-cell loss or failure, as seen in type 1 diabetes mellitus, late-stage type 2 diabetes, or following total pancreatectomy. Low C-peptide with hypoglycemia and elevated insulin is consistent with exogenous insulin use or insulin secretagogue ingestion.
Insulin and C-peptide are relevant to athletes primarily for metabolic health and recovery monitoring rather than direct performance metrics. Elevated fasting insulin or C-peptide may indicate insulin resistance, which can impair recovery, increase injury risk, and compromise metabolic efficiency; conversely, well-controlled insulin sensitivity supports nutrient partitioning, glycogen repletion, and sustained endurance performance.
Turnaround Time
4 days (up to 8 days)
Fasting Required
No
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$18.00
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