C-peptide blood test in Chiswick

What the test measures

When the pancreas makes insulin, it first produces a larger molecule called proinsulin, which is then split into insulin and C-peptide. The two are released into the blood in equal amounts. Insulin is cleared quickly by the liver, while C-peptide stays in the blood for longer, so measuring it gives a steadier picture of how much insulin your pancreas is producing.

C-peptide is useful because it is not affected by insulin injections, so it shows your own insulin production even if you use insulin treatment. Clinicians use it to help tell type 1 diabetes, where insulin production falls, from type 2 diabetes, where production is often normal or high but the body responds less well. It can also support the assessment of insulin resistance and some causes of low blood sugar. The price includes the blood sample taken at our Chiswick clinic, analysis at the Randox accredited laboratory, a review of your result with an Omnia practitioner and a GP feedback report on request.

Who it is for

• You have diabetes and you or your clinician want to understand how much insulin you still make.
• You have signs of insulin resistance, such as weight around the middle, and want more detail than glucose alone.
• You have episodes of low blood sugar, such as shakiness and sweating, and want to look at causes.
• You have prediabetes or a raised HbA1c and want a fuller metabolic picture.
• You have polycystic ovary syndrome and want to understand your insulin levels.

Understanding your result

Your report shows your C-peptide with the laboratory reference range. A low level suggests the pancreas is making less insulin, which is seen in type 1 diabetes or longer-standing type 2 diabetes. A high level suggests the pancreas is working harder than usual, often because of insulin resistance, and is read together with your glucose and HbA1c.

Kidney function affects C-peptide because the kidneys clear it, so it is interpreted with your kidney results too. If you have frequent low blood sugar episodes, please speak to your GP. Any figure outside the range is a talking point with your practitioner, not a conclusion.

Preparing for your test

Please fast for 8 to 12 hours before your sample, drinking water only, as food raises C-peptide. Book a morning appointment if you can. If you have diabetes and take insulin or tablets that can cause low blood sugar, ask your GP or diabetes team how to manage your medicines while fasting, and do not stop them without advice.

C-peptide is included in our Diabetes Status check with HbA1c and glucose, and in Tired All The Time. Our listings include every blood test and price in Chiswick.

Questions

How much is a C-peptide blood test in Chiswick?

The C-peptide blood test costs £129. That includes your sample at our Chiswick clinic, analysis at an accredited laboratory, a practitioner review and a GP feedback report on request.

Do I need to fast for C-peptide?

Yes. A fasting sample of 8 to 12 hours, water only, gives the most reliable result, because eating raises insulin and C-peptide.

How is C-peptide different from insulin?

Both are released together, but C-peptide stays in the blood longer and is not affected by insulin injections, so it is a more stable measure of your own production.

Can C-peptide tell which type of diabetes I have?

It can help. Low levels support type 1 diabetes and normal or high levels are more typical of type 2, but the diagnosis is made by your GP or diabetes team using several factors.