Biomarker guide · Metabolic health
A C-peptide blood test shows how much insulin your pancreas is actually making. In the UK you can get it privately in TrueVitals Ultimate (£399 including the clinic draw, 140 biomarkers), where it sits alongside fasting insulin, glucose, HbA1c and the HOMA-IR insulin resistance score. It is not in our Advanced panel.
When your pancreas makes insulin, it cuts one long molecule (proinsulin) into two pieces: insulin and C-peptide. They leave the pancreas in equal amounts. Insulin is cleared quickly by the liver, but C-peptide stays in the blood longer and more steadily, so it is a cleaner read on how hard your pancreas is working.
That makes it useful in two situations: telling apart the main types of diabetes, and spotting a pancreas that is pumping out extra insulin to keep blood sugar normal, which is the hidden stage of insulin resistance.
One result never diagnoses diabetes. A GP diagnoses it from HbA1c or glucose; C-peptide helps explain the picture.
Fasting C-peptide is commonly reported in the region of 0.3 to 1.3 nmol/L (about 300 to 1,300 pmol/L), but ranges and units differ between labs. Your TrueVitals report always uses the lab's own range for your sample and explains where you sit within it.
| Option | Includes it | Price | What else you get |
|---|---|---|---|
| TrueVitals Ultimate | Yes | £399 incl. clinic draw (home visit £29 extra) | With fasting insulin, glucose, HbA1c, HOMA-IR and HOMA-B. Clinician-reviewed report in 4 working days. |
| TrueVitals Signature | Yes | £799 incl. draw | 230 biomarkers at Randox Health clinics, up to 12 working days. |
| TrueVitals Advanced | No | £319 | Not included. Advanced has glucose and HbA1c but not insulin or C-peptide. |
| NHS GP | On request | Free if clinically indicated | Usually only requested to classify diabetes, not for insulin resistance checks. |
TrueVitals prices checked 5 November 2026. Every TrueVitals report is clinician-reviewed. Pay in instalments with Klarna or Clearpay. Book a draw at one of 103 partner clinics, or add a home visit.
When you should not use a private test: if you have symptoms of high blood sugar (heavy thirst, passing a lot of urine, weight loss you can't explain, blurred vision), see your GP or call 111 the same day. That needs urgent glucose testing, not a booked panel.
A private panel is a good way to get a baseline, understand a result in context and track it over time. It does not replace your GP for symptoms, and anything that needs follow-up is flagged in plain words in your report.
C-peptide on its own rarely tells the whole story. In TrueVitals panels it is reported with these related markers:
Yes. Fast for 8 to 12 hours beforehand (water is fine) and book a morning appointment. Eating raises C-peptide, so a non-fasted result is hard to read. Our fasting guide covers the details.
They answer slightly different questions, which is why Ultimate measures both. C-peptide is steadier and is not affected by insulin injections; fasting insulin is used for the HOMA-IR score. Read together with glucose they give a fuller picture than either alone.
In TrueVitals Ultimate it comes as part of 140 biomarkers for £399 including the clinic blood draw. Some clinics sell it on its own, but you would still need glucose and insulin alongside it to interpret it properly.
It helps. Low C-peptide points towards little insulin production, as in type 1 or LADA; normal or high points towards type 2. A diagnosis of type should be made by your GP or diabetes team, often with antibody tests too.
No. C-peptide, fasting insulin and the HOMA scores are in Ultimate and Signature only. Use our panel comparison to check any marker.
Yes. C-peptide is cleared by the kidneys, so reduced kidney function can push it up. Ultimate includes creatinine, eGFR and cystatin C, so your report reads C-peptide in that context.
How this page was written: by James Smillie, founder of TrueVitals, reviewed by the TrueVitals clinical review team, using NHS and laboratory reference sources. Ranges are typical values; your report uses your lab's own ranges. TrueVitals sells the panels named on this page, so we have stated plainly what this test cannot do. Last updated 5 November 2026.
Ultimate: 140 biomarkers (139 for women), £399 including the clinic draw, home visit £29 extra. Clinician-reviewed report within 4 working days.
Clinical trust, built in
Included in the price, never an add-on. We consider it essential.
We've had GPs, surgeons and specialist doctors trust us for their own bloods.
Metabolic health, menopause specialists and more, ready if your results need a closer look.
Meet our specialists →We use cookies to help improve your experience. Learn more
Keep you signed in and let checkout work. The site needs these.
Help us see which pages are useful and where people come from. No advertising, nothing sold.
.png)