Vitamin C (Ascorbic Acid)
Measures vitamin C (ascorbic acid) in plasma, mostly to check whether you are low on this vitamin.
AI-verified against cited sources. Awaiting expert reviewAlso called Vit CLOINC 1903-4
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What it is
Vitamin C helps your body make collagen, heal wounds, absorb iron from plant foods and protect cells from damage. You get it from fruits and vegetables such as citrus, peppers, kiwi and broccoli. Your body can't make it and stores little. In healthy people, blood levels rise with intake and then level off at about 70-80 µmol/L (1.2-1.4 mg/dL).
Why it matters
Severe, long-lasting vitamin C deficiency causes scurvy, with bleeding gums, easy bruising, tiny red spots around hair follicles, joint pain and slow wound healing. Scurvy is uncommon but still occurs, especially in people who eat very restricted diets. The test is mostly used when deficiency is suspected.
If it’s low
A low result means you have less vitamin C available than most people. Levels under 11 µmol/L (about 0.2 mg/dL) are considered deficiency, and levels from 11 to 23 µmol/L (about 0.2-0.4 mg/dL) are linked with a moderate risk of deficiency, according to ARUP. A sample that wasn't kept cold and out of light can also read falsely low.
Common causes
- A diet with few fruits and vegetables, or a very restricted diet
- Smoking, which raises how much vitamin C the body uses
- Infection or other illness
- Alcohol use
- Problems absorbing food or a poor appetite
- A sample that was warm, exposed to light, or delayed before freezing
What can help
- Talk with a clinician about the cause and whether a vitamin C supplement is right for you
- Include vitamin C-rich foods such as citrus, strawberries, peppers, kiwi and broccoli
- If you smoke, ask your clinician about support to quit
If it’s high
A high result almost always reflects recent vitamin C supplements, high-dose vitamin C drinks or IV vitamin C. Blood levels level off with oral intake because the gut absorbs less and the kidneys clear the extra, so a very high level suggests a recent large dose. Large doses can cause stomach upset and loose stools.
Common causes
- Vitamin C supplements, including powders and drinks sold for immune support
- Vitamin C given through an IV
- A blood draw soon after a large dose
What can help
- Tell your clinician about all supplements you take, including drinks and powders
- Ask whether your current vitamin C intake makes sense for you
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
For adults: 0.4–2 mg/dL. Source: Mayo Clinic Laboratories, ARUP Laboratories, Fullscript (listing Quest Diagnostics test data), Nutrients.
- Adults (this one applies)0.4–2 mg/dL
Sources: Mayo Clinic Laboratories, ARUP Laboratories, Fullscript (listing Quest Diagnostics test data), Nutrients
See Vitamin C by age and sex, with the U.S. survey numbers where they exist.
ARUP interpretive categories for plasma vitamin C
- Deficiencybelow 11 µmol/L
- Moderate risk of deficiency (inadequate tissue stores)11 to under 23 µmol/L
- Above the deficiency-risk cutoffs23 and above µmol/L
How common is your level?
NHANES describes the US civilian, non-institutionalized population, not a 'healthy' reference group. People with disease, on medication, fasting or not (except fasting-subsample markers), smokers and so on are all included. A percentile says where a value sits among Americans of that sex and age, not whether it is normal.
Use the left and right arrow keys to read each age. Shift moves five years.
Reference data derived from CDC/NCHS National Health and Nutrition Examination Survey (NHANES), cycles 2017-2018. Analysis by bloodtesttracker.com; not endorsed by CDC, NCHS or HHS.
Explore Vitamin C by age and sex: every percentile as a table, with a download.
What can affect your result
- Sample handling: it must be chilled right away, protected from light and frozen
- Fasting: Mayo Clinic Laboratories asks for 12 hours; ARUP prefers a fasting sample
- Recent supplements, vitamin C drinks or IV vitamin C
- Smoking, pregnancy, infection and other illness raise the body's needs
- Vitamin C breaks down quickly after the draw. The sample must be put on ice right away, protected from light, and frozen; thawing and refreezing or light exposure lowers the result.
- Heparin plasma is required. EDTA plasma and whole blood are not acceptable (ARUP).
- Recent vitamin C supplements, drinks or IV vitamin C raise the result.
- Smoking, infection and other illness increase turnover and can lower levels.
Morning, after an overnight fast. Reflects recent intake. Blood levels level off at about 70-80 umol/L (1.2-1.4 mg/dL) no matter how much more is taken by mouth.
When to talk to a clinician
Contact a clinician if you have bleeding gums, easy bruising, small red or blue spots around hair follicles, new joint or leg pain, or wounds that heal slowly, especially if your diet is very limited. Get urgent care for heavy bleeding.
Questions you could ask
- Do smoking, my diet or any health conditions affect how much vitamin C I need?
- Could a supplement, drink or IV vitamin C explain this result?
- Is my current vitamin C intake still right for me?
- What might be causing my level to be low?
- Should we recheck it, and could the way the sample was handled have affected it?
Questions people ask
Why did my lab ask for the blood to be put on ice?
Vitamin C breaks down quickly after blood is drawn, especially when warm or in light. Labs chill, protect and freeze the sample so the result reflects what was in your blood. A delay can make a result read falsely low.
Does taking more vitamin C keep raising my blood level?
No. In healthy people, blood levels level off at about 70-80 µmol/L (1.2-1.4 mg/dL), because the gut absorbs less and the kidneys clear the extra. IV vitamin C can push levels much higher.
How do I convert mg/dL to µmol/L?
Multiply mg/dL by 56.78. For example, 0.8 mg/dL is about 45 µmol/L. To go the other way, multiply µmol/L by 0.0176.
Show the science and sources
Units
- 1 mg/dL = 1 mg/dL
- 1 mg/dL = 56.78 µmol/L
- 1 mg/dL = 10 mg/L
Open the Vitamin C unit converter
Is a change real?
Vitamin C naturally varies about 20% from test to test in the same healthy person. Between two results from the same lab, a rise of 85% or more, or a fall of 46% or more, is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Desirable Biological Variation Database specifications, 2014 update (Minchinela J, Ricos C, et al.; the 'Ricos database', a compilation of median published CVI/CVG).
For clinicians and researchers
Ascorbate is measured by LC-MS/MS in heparinized plasma (Mayo) and reported as ascorbic acid; it oxidizes rapidly to dehydroascorbate, so labs require immediate chilling, light protection, rapid processing and freezing. Mayo reports 0.4-2.0 mg/dL and ARUP 23-114 umol/L (multiply umol/L by 0.0176 for mg/dL); Quest reports 0.2-2.1 mg/dL for men and 0.3-2.7 mg/dL for women. Plasma follows saturable kinetics: with rising oral intake, plasma plateaus at about 70-80 umol/L, with an intake of about 200-400 mg/day saturating blood in healthy people, and intravenous dosing bypasses the absorption limit. ARUP defines below 11 umol/L as deficiency and 11-23 umol/L as moderate risk from inadequate tissue stores; US NHANES reports use below 11.4 and below 23 umol/L, and scurvy reviews generally treat below about 11 umol/L as severe biochemical deficiency. Thresholds vary in the literature. Leukocyte vitamin C is an alternative that reflects tissue stores but is rarely offered.
LOINC 1903-4 (primary), 14622-5. Specimen: plasma.
Sources
- Ascorbic Acid (Vitamin C), Plasma - Test ID VITC (Mayo Clinic Laboratories Extended Catalog), Mayo Clinic Laboratories
- Vitamin C (Ascorbic Acid), Plasma (test 0080380), ARUP Laboratories
- The Prevalence of Nutritional Imbalances in the US Population Over Time: Biomarker Data from the Cross-Sectional National Health and Nutrition Examination Survey (NHANES 1999-2000 through August 2021-August 2023), Current Developments in Nutrition (2026)
- Contemporary Scurvy in Vulnerable Populations in High-Income Countries: A Systematic Review and Multilevel Meta-Analysis, Nutrients (2026)
- The Pharmacokinetics of Vitamin C, Nutrients (2019)
- Micronutrient, Vitamin C (Quest Diagnostics test, adult intervals as listed by Fullscript), Fullscript (listing Quest Diagnostics test data)
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.