A blood or urine test to measure your C-peptide level is a way to help your healthcare provider understand how well your body is producing insulin. It can help them diagnose and treat diabetes, or other diseases that involve how your body makes insulin.
About Insulin Peptide
A peptide hormone, insulin is made by the cells that make it in your pancreas (called the islets of Langerhans). Its chemical structure includes a molecular weight of 5808 Da and 51 amino acids.
In humans, it is produced by a type of cell called b-cells in the islets. Normally, b-cells secrete insulin in a small amount, but in people with type 1 diabetes the amount of insulin secreted by the b-cells can be abnormally high.
Insulin binds to receptors on the outside of cells, initiating glucose uptake and inhibiting gluconeogenesis, glycogenolysis, and ketogenesis. It has a short half-life in the liver and is quickly degraded by the kidneys.
When insulin is cleaved from proinsulin, a small amount of a peptide called C-peptide is released into the bloodstream. The peptide is mainly excreted in the urine and has a longer half-life than insulin.
Identifying Human Islet Immune Proteins
Some T cells recognize specific molecules in the islets that are made by the insulin peptide-producing b-cells of human organ donors without diabetes. These are called HIPs, which have a fragment of insulin C-peptide on one side and natural cleavage products on the other. These HIPs include a 2.5HIP, a peptide formed between a left insulin C-peptide fragment and the N termini of WE14, and a 6.9HIP, a peptide formed by a left insulin C-peptide fragment linked to the N termini of a natural cleavage product from pro-islet amyloid polypeptide (IAPP2).