C-peptide

C-peptide is a substance made by the pancreas as a byproduct of producing insulin. Each time the pancreas releases insulin, it releases an equal amount of C-peptide, so measuring C-peptide gives a reliable picture of how much insulin your body is making of its own accord. It is particularly useful because, unlike insulin itself, it is not affected by any insulin given as medication.

What it can help assess

• How well your pancreas is producing insulin: low levels suggest the pancreas is making little or no insulin, while high levels suggest it is producing a lot
• Distinguishing types of diabetes: it can help tell apart type 1 diabetes, where insulin production is very low, from type 2 diabetes, where the body often still produces insulin but uses it less effectively
• Investigating low blood sugar (hypoglycaemia): it helps identify whether unexplained low blood sugar is due to the body overproducing insulin
• Monitoring pancreatic function over time in people with known diabetes

Why it matters

Understanding how much insulin your body produces naturally provides valuable insight into how your blood sugar is regulated. This can support a clearer diagnosis, guide the most appropriate management, and help build a fuller picture of your metabolic health.