What is the C-Peptide test?

The C-Peptide blood test measures the level of C-peptide released into the bloodstream when insulin is produced by the pancreas. C-peptide is formed in equal amounts to insulin, making it a reliable marker of endogenous (natural) insulin production.

Unlike insulin levels, which can fluctuate rapidly or be affected by injected insulin, C-peptide provides a more stable and accurate reflection of how well the pancreas is functioning. For this reason, it is widely used in diabetes assessment and metabolic investigations.

The test is commonly requested in endocrinology, diabetes care, and when evaluating unexplained blood sugar abnormalities.

Why do I need a C-Peptide test?

C-Peptide testing helps determine whether the body is producing enough insulin and whether insulin deficiency or resistance is contributing to abnormal glucose levels.

It is particularly valuable when diagnosing diabetes type, assessing insulin dependence, or evaluating pancreatic function.

You may need a C-Peptide test if you:

• Have diabetes or prediabetes
• Need to differentiate type 1 and type 2 diabetes
• Are experiencing unexplained hypoglycaemia
• Are using insulin and need to assess residual pancreatic function
• Have poor blood sugar control despite treatment
• Are being assessed for insulin resistance
• Have suspected pancreatic dysfunction

Symptoms that may prompt testing include:

• Frequent urination
• Excessive thirst
• Fatigue
• Unexplained weight loss or gain
• Episodes of low blood sugar

Benefits of the C-Peptide test

• Assesses natural insulin production
  Reflects how much insulin the pancreas is making.
• Differentiates diabetes types
  Helps distinguish type 1 from type 2 diabetes.
• Unaffected by injected insulin
  More reliable than insulin levels alone.
• Evaluates pancreatic beta-cell function
  Useful in long-term diabetes management.
• Supports treatment decisions
  Guides insulin and medication strategies.
• Helps investigate hypoglycaemia
  Assists in identifying insulin overproduction.
• Widely clinically recognised
  Used in standard endocrine practice.
• Simple blood test
  Requires only a single blood sample.

Step by step – how the test works

You can access C-Peptide testing UK-wide through two options:

1. Clinic appointment
   Choose your nearest UK clinic, where a healthcare professional will take your blood sample.
2. At-home or hotel visit (£60 extra)
   A qualified phlebotomist comes to your home or hotel, so you don’t need to travel.

Your sample is analysed in an accredited UK laboratory, and results are delivered securely.

Your results explained

Low C-Peptide levels

Suggest reduced or absent insulin production, commonly seen in type 1 diabetes or advanced type 2 diabetes.

Typical UK reference range:

• < 0.5 ng/mL (low insulin production)

Normal C-Peptide levels

Indicate normal pancreatic insulin production.

Typical UK reference range:

• 0.5–2.0 ng/mL

High C-Peptide levels

Suggest increased insulin production, often associated with insulin resistance, early type 2 diabetes, or metabolic syndrome.

Typical UK reference range:

• > 2.0 ng/mL

Reference ranges may vary slightly between laboratories and testing conditions.