Vitamins and nutrition . Patient guide
Vitamin C Blood Test
What is Vitamin C
Vitamin C (ascorbic acid) is an essential antioxidant needed for collagen formation, wound healing, immune function and iron absorption. The body cannot make or store much of it, so status depends on regular dietary intake.
This biomarker entry is being clinically reviewed by our team. The factual content draws on UK guidance (NICE, NHS, Royal Colleges and the relevant speciality society where cited).
Reference range
Reported in µmol/L. Final reports always carry the issuing laboratory's range, which is what your clinician will interpret against.
| Group | Range | Note |
|---|---|---|
| Adults (plasma) | approx. 28 to 85 | µmol/L; varies between labs |
What it is
Vitamin C is obtained from fruit and vegetables and is used across the body, notably in making collagen, the protein that holds skin, gums, blood vessels and connective tissue together. Because there is no large store, levels fall within weeks of poor intake.
Why a clinician would order it
Vitamin C is checked in suspected deficiency (poor diet, restrictive eating, alcohol dependence, malabsorption), in poor wound healing or unexplained bruising and bleeding gums, and in some fatigue work-ups. Frank deficiency (scurvy) is uncommon but still seen.
If your level is outside the range
Symptoms of low Vitamin C
- Tiredness
- Bleeding or swollen gums
- Easy bruising
- Slow wound healing
- Rough or bumpy skin
What low can indicate. Inadequate intake of fruit and vegetables, restrictive diets, smoking (which increases requirements), alcohol dependence, or malabsorption. Prolonged deficiency causes scurvy.
Symptoms of high Vitamin C
- Excess is usually excreted; very high supplemental intake can cause diarrhoea and may raise the risk of kidney stones in susceptible people
What high can indicate. Recent high-dose supplementation. Vitamin C is water-soluble, so excess is largely excreted rather than stored.
Testing tips
Avoid vitamin C supplements for 24 hours before testing for a true baseline. The sample needs careful handling as vitamin C degrades quickly, which the lab accounts for.
Sources
UK guidance our clinicians use when interpreting this marker.
This page is general patient information, not personal medical advice. A GMC-registered clinician will review your results and tailor any interpretation to you. See our Editorial Policy for how we write and review content.
Common questions about Vitamin C
What is a normal Vitamin C range?
Adults (plasma): approx. 28 to 85 (µmol/L; varies between labs). Always interpret your own results against the laboratory range printed on your report, since assay-specific reference ranges vary.
What does a low Vitamin C result mean?
Inadequate intake of fruit and vegetables, restrictive diets, smoking (which increases requirements), alcohol dependence, or malabsorption. Prolonged deficiency causes scurvy.
What does a high Vitamin C result mean?
Recent high-dose supplementation. Vitamin C is water-soluble, so excess is largely excreted rather than stored.
Do I need to fast or prepare for the Vitamin C blood test?
Avoid vitamin C supplements for 24 hours before testing for a true baseline. The sample needs careful handling as vitamin C degrades quickly, which the lab accounts for.
Can I order a Vitamin C blood test privately in London?
Yes. WMG Health offers Vitamin C as part of bespoke panels and several pre-built panels at our 134 Harley Street clinic. Results are clinician-reviewed by a GMC-registered doctor within 4 hours for the most common assays. All panels are custom-built around your specific question; bookings via /contact/ or 020 3239 3378.