C-peptide

C-peptide is a small protein that your body makes when it produces insulin. Insulin is a vital hormone that helps your body use sugar (glucose) for energy. When your pancreas makes insulin, it's initially produced as a larger molecule called proinsulin. This proinsulin is then split into two parts: insulin itself and C-peptide. They are released into the bloodstream in equal amounts.

What it is

Think of C-peptide as a helpful indicator. Because your body releases C-peptide and insulin in the same amounts, measuring C-peptide levels in your blood gives doctors a good idea of how much insulin your pancreas is making on its own. It's a more stable marker than insulin itself, which can be quickly used up or affected by external insulin injections.

Why it matters

Understanding your body's natural insulin production is important for several reasons, particularly if you have or are at risk of diabetes.

Diabetes is broadly categorised into types based on how the body handles insulin. In Type 1 diabetes, the body's immune system mistakenly attacks and destroys the insulin-producing cells in the pancreas. This means the pancreas can't make much, if any, insulin. Measuring C-peptide can help confirm this lack of insulin production.

In Type 2 diabetes, the body either doesn't produce enough insulin or the body's cells don't respond properly to the insulin that is produced (this is called insulin resistance). C-peptide levels can help doctors understand the stage of Type 2 diabetes and how well the pancreas is coping over time.

Monitoring C-peptide can also be useful in other situations, such as investigating the cause of low blood sugar (hypoglycaemia) or assessing the function of the pancreas after certain medical conditions or treatments.

What can cause it to be high or low

Higher than expected C-peptide levels can be associated with:

• Insulin resistance: This is common in Type 2 diabetes, where the pancreas works harder to produce more insulin to try and overcome the body's resistance to it.
• Certain pancreatic tumours: Very rarely, tumours of the pancreas can produce excess insulin and therefore excess C-peptide.
• Taking certain medications: Some medications can influence insulin production or C-peptide levels.

Lower than expected C-peptide levels can be associated with:

• Type 1 diabetes: As the insulin-producing cells are destroyed, the body makes very little C-peptide.
• Pancreatic damage or disease: Conditions that damage the pancreas can reduce its ability to produce insulin and C-peptide.
• Long-standing Type 2 diabetes: Over many years, the pancreas may become exhausted and produce less insulin.

The typical reference range for C-peptide in the UK is usually between 1.1 and 4.4 nanograms per millilitre (ng/ml), though this can vary slightly between laboratories.

Lifestyle factors that may help

For individuals with conditions where C-peptide levels might be influenced, certain lifestyle approaches can be beneficial and are often discussed with healthcare professionals:

• Healthy Eating Patterns: Focusing on a balanced diet rich in whole foods, fruits, vegetables, and lean proteins, while managing carbohydrate intake, can support overall metabolic health.
• Regular Physical Activity: Engaging in regular exercise can improve insulin sensitivity, helping the body use glucose more effectively.
• Weight Management: Maintaining a healthy weight, or losing excess weight if needed, can have a significant positive impact on insulin function and pancreatic health.
• Stress Management: Chronic stress can affect hormone levels, including those related to blood sugar control. Exploring techniques to manage stress may be helpful.
• Adequate Sleep: Ensuring sufficient, good-quality sleep is important for hormonal balance and overall well-being.

Questions to discuss with your GP

If you have had a C-peptide test or are concerned about your body's insulin production, here are some questions you might find helpful to discuss with your GP:

• What do my C-peptide results mean in the context of my overall health?
• Could my C-peptide levels indicate a specific type of diabetes or another condition?
• What are the next steps or further tests recommended based on my results?
• How might lifestyle changes, such as diet and exercise, affect my C-peptide levels and diabetes management?
• Are there any specific symptoms I should be aware of that might be related to my C-peptide levels?
• How often should my C-peptide levels be monitored, if at all?