Human C-peptide of insulin is an amino acid chain of 3000 molecular weight, joining the A and B chains of insulin. It is secreted from the granules in the islet beta cells at equimolar concentrations with insulin. It is however not as rapidly degraded by the liver as in the case of insulin, and therefore is more stable in the blood. These characteristics make the determination of C-peptide an advantageous test as an indicator to quantify insulin. It is therefore used in evaluating hypoglycemia and insulnoma.