Riboflavin (Vitamin B2) Unit Converter
Riboflavin (Vitamin B2) Unit Converter
Convert plasma riboflavin between µg/L, ng/mL and nmol/L — and read the result knowing that a plasma level mostly reports what the patient ate yesterday, while functional status is measured by the erythrocyte glutathione reductase activation coefficient.
Riboflavin (Vitamin B2) converter
Mass ⇄ molarFasting plasma riboflavin 8 µg/L
The conversion
µg/L = nmol/L ÷ 2.65703
because 2.65703 = 1 µg/L ÷ 376.36 g/mol, the molecular weight of riboflavin
- µg/L = ng/mL
- identical concentrations written two ways; no arithmetic between them
- MW 376.36
- riboflavin, C₁₇H₂₀N₄O₆. Plasma assays report free riboflavin; the coenzyme forms FMN and FAD, which carry most of the body's riboflavin, are heavier and are measured separately where they are measured at all
- why fasting matters to the number
- riboflavin absorption is rapid and the plasma level rises within hours of a meal or a supplement. Mayo's reference interval was established on 12-hour fasting specimens, so a non-fasting result is not comparable with it
- light
- riboflavin is strongly photolabile — this is the same chemistry that degrades it in milk left in sunlight. Samples go into an amber vial and the plasma is separated within two hours
Worked example
Fasting plasma riboflavin 8 µg/L
8 µg/L = 8.00 ng/mL — the same number
8 × 2.65703 = 21.26 nmol/L
21.26 nmol/L is inside Mayo's 1–19 µg/L interval, which is 2.66–50.48 nmol/L
Going back: 21.26 ÷ 2.65703 = 8.00 µg/L
What the number does not tell you is whether the tissues are replete. A patient who took a B-complex tablet yesterday and one who has been eating well for a year can produce the same figure
Two ways of asking about riboflavin, and what each answers
| Measurement | What it reflects | Deficiency is indicated by |
|---|---|---|
| Plasma or serum riboflavin | Intake over roughly the last day or two | A low value, in a fasting sample — Mayo take under 1 µg/L as deficient |
| EGRAC — erythrocyte glutathione reductase activation coefficient | Functional riboflavin status in tissue, over the life of the red cell | A coefficient above about 1.4; values near 1.0 indicate repletion |
| Urinary riboflavin excretion | Saturation of the body pool and recent intake | Low excretion, but it is strongly diet-dependent and rarely used clinically |
Where riboflavin deficiency turns up
| Setting | Why |
|---|---|
| Poor or restricted diets, especially with little dairy or fortified cereal | Milk and fortified cereals are the dominant dietary sources in most Western diets |
| Chronic alcohol use | Reduced intake and impaired absorption together |
| Malabsorption, short bowel, prolonged parenteral nutrition without adequate vitamins | Absorption is in the proximal small bowel and is carrier-mediated and saturable |
| Rare inborn errors — riboflavin transporter deficiency (Brown-Vialetto-Van Laere syndrome) | A treatable neurological disorder in which high-dose riboflavin is the treatment; a plasma level is not how it is diagnosed |
A level that reports yesterday, and a test that reports the tissues
Riboflavin is reported as a mass concentration in micrograms per litre — the same number as nanograms per millilitre — or in nanomoles per litre. The bridge is riboflavin’s molecular weight, 376.36, so one microgram per litre is 2.65703 nanomoles per litre. The arithmetic is the easy part of this page. The harder part is what the number means.
Plasma riboflavin is a short-memory measurement. Absorption is rapid, the circulating pool is small, and the surplus is cleared in the urine — which is why a B-complex tablet turns urine a vivid yellow within hours. A plasma level therefore tracks intake over roughly the last day or two rather than the state of the tissues. Mayo’s reference interval, 1 to 19 micrograms per litre, was established on 12-hour fasting specimens for exactly this reason, and they note that a non-fasting sample or one taken after supplementation can be reported as elevated without anything being wrong. A result that arrives without knowing whether the patient was fasting is close to uninterpretable at the upper end.
Where functional status is the question — is this person’s riboflavin-dependent enzyme chemistry actually impaired — the measurement to ask for is the erythrocyte glutathione reductase activation coefficient, the EGRAC. Glutathione reductase needs flavin adenine dinucleotide as its cofactor, so the assay measures the enzyme’s activity in a red cell lysate with and without added FAD and takes the ratio. In repletion the enzyme is already saturated and adding FAD changes little, giving a coefficient near 1.0; in deficiency a large pool of apoenzyme is waiting for cofactor and the added FAD raises activity sharply, pushing the coefficient above about 1.4. It reflects status over the lifespan of the red cell rather than over yesterday, which is why nutrition research uses it in preference to a plasma level. It is unreliable in glucose-6-phosphate dehydrogenase deficiency.
Both the plasma sample and the vitamin itself are photolabile. Riboflavin is a strong photosensitiser — the same chemistry that spoils milk in sunlight — so the specimen goes into an amber vial, the plasma is separated within about two hours, and it is kept light-protected until it is analysed. A sample left on a windowsill loses riboflavin and is reported low.
Frequently asked questions
How do you convert riboflavin from µg/L to nmol/L?
Multiply by 2.65703, which is one microgram per litre divided by riboflavin’s molecular weight of 376.36 g/mol. A plasma riboflavin of 8 µg/L is 21.26 nmol/L. Divide by the same factor to go back, and remember that µg/L and ng/mL are the same number.
What is EGRAC and why is it better than a plasma riboflavin?
The erythrocyte glutathione reductase activation coefficient measures the activity of a FAD-dependent enzyme in red cells with and without added FAD, and reports the ratio. A coefficient near 1.0 means the enzyme is already saturated with cofactor; one above roughly 1.4 means a large pool of apoenzyme is waiting for it, which is functional deficiency. It reflects tissue status over the life of the red cell, where a plasma level reflects the last day or two of intake.
Does the sample have to be fasting?
For the reference interval to apply, yes. Riboflavin is absorbed quickly and plasma concentrations rise within hours of a meal, a fortified food or a supplement, so Mayo established their interval on 12-hour fasting specimens and note that a non-fasting sample can be reported as elevated. A high riboflavin in a non-fasting patient usually means nothing at all.
Is a high riboflavin dangerous?
No toxicity has been established. Absorption is saturable and the excess is excreted in the urine, which is why high-dose supplements produce bright yellow urine. High-dose riboflavin is used therapeutically in migraine prophylaxis and in riboflavin transporter deficiency without the level itself causing concern.
Why does the sample need protecting from light?
Riboflavin is strongly photolabile, so light exposure between collection and analysis destroys some of the vitamin and the result is reported falsely low. Laboratories ask for an amber vial, separation of plasma within about two hours, and light-protected storage for that reason.
Related calculators
References
- Mayo Clinic Laboratories. Test ID: VITB2 — Riboflavin (Vitamin B2), Plasma. Reference values 1–19 mcg/L; 12-hour fast required; amber vial, light protected.
- Institute of Medicine. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington DC: National Academies Press; 1998. Riboflavin chapter — erythrocyte glutathione reductase activity coefficient as the functional indicator.
- Powers HJ. Riboflavin (vitamin B-2) and health. Am J Clin Nutr. 2003;77(6):1352–1360.
- Bosch AM, Abeling NGGM, IJlst L, et al. Brown-Vialetto-Van Laere and Fazio Londe syndrome is associated with a riboflavin transporter defect. J Inherit Metab Dis. 2011;34(1):159–164.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.