C-peptide testing

You may have seen a recent story on BBC news about a blood test for people with diabetes.  This blood test is called C peptide and you can find the BBC news report by clicking here.

C-peptide gives us an indication of the amount of insulin that the pancreas is able to make itself.

What is the purpose of the blood test?

It is usually very easy to make a diagnosis of diabetes, as the diagnosis is based simply on the affected person having a raised blood glucose (sugar) level.  Diabetes can have many different causes, but the most common causes are Type 2 and Type 1 diabetes.

Establishing the cause of diabetes is usually straightforward. However, some people fall into a ‘grey area’, with features of both type 1 and type 2 diabetes. The C peptide test is being used in our unit in order to help us establish if the diagnosis of Type 1 diabetes is accurate. Not everyone will need this test, as it may be that the diagnosis of Type 1 diabetes is not in any doubt. It is also not possible to interpret the test with certainty in people who have had diabetes for less than 3 years.

What would happen if the C-peptide test showed that someone did not have Type 1 diabetes?

Most people who have a diagnosis of Type 1 diabetes will have that diagnosis confirmed by the C-peptide blood test. However, a small number of people may be found not to have Type 1 diabetes. In that situation, further tests are usually needed to determine the underlying cause of the person’s diabetes. Once the cause of a person’s diabetes is established, it is sometimes possible to alter the treatment needed to control your blood sugar levels.

How can I access a C-peptide blood test?

We are not able to test people unless they are NHS Lothian patients.  If you think you or a family member would benefit from having this test you would need to discuss this with your own diabetes team.  NHS Lothian diabetes teams can offer this test when people come to hospital for their routine appointments but we are not able to bring appointments forward for the purposes of checking a C peptide.