Thiamine (Vitamin B1) Unit Converter
Thiamine (Vitamin B1) Unit Converter
Convert whole-blood thiamine between µg/L, ng/mL and nmol/L using the molecular weight of thiamine diphosphate — the coenzyme the assay actually measures, and the reason a factor taken from free thiamine is 1.6 times wrong.
Thiamine (Vitamin B1) converter
Mass ⇄ molarWhole-blood thiamine diphosphate 50 µg/L
The conversion, and the molecular weight it has to use
µg/L = nmol/L ÷ 2.35123
because 2.35123 = 1 µg/L ÷ 425.31 g/mol, the molecular weight of thiamine diphosphate
- µg/L = ng/mL
- a microgram per litre and a nanogram per millilitre are the same concentration, so no arithmetic is needed between them. Laboratories in the United Kingdom usually report nmol/L; µg/L and ng/mL appear on some North American and research reports
- MW 425.31 — thiamine diphosphate
- also called thiamine pyrophosphate or TDP. This is the active coenzyme, the form that sits in transketolase, pyruvate dehydrogenase and 2-oxoglutarate dehydrogenase, and the form that makes up the great majority of the thiamine in whole blood. It is what a whole-blood assay is calibrated to report
- MW 265.35 — free thiamine, the wrong number here
- free (unphosphorylated) thiamine is a smaller molecule, so it gives a larger factor: 3.76865 nmol/L per µg/L instead of 2.35123. Using it on a whole-blood result inflates the molar figure by 425.31 ÷ 265.35 = 1.603, which is enough to carry a value across the top of the reference interval
- the specimen
- EDTA whole blood, protected from light. Roughly four-fifths of circulating thiamine is inside the red cells as the diphosphate, so a serum or plasma thiamine measures a small, labile and largely uninformative fraction
Worked example
Whole-blood thiamine diphosphate 50 µg/L
50 µg/L = 50.00 ng/mL — the same concentration written the other way
50 × 2.35123 = 117.6 nmol/L, using the molecular weight of thiamine diphosphate (425.31)
117.6 nmol/L sits inside Mayo's 70–180 nmol/L interval for whole blood
Now do it wrongly: 50 × 3.76865, the factor from free thiamine's 265.35, gives 188.4 nmol/L — above the interval. The same sample, converted with the wrong molecular weight, reads as a high thiamine rather than a mid-normal one
The error runs the other way too. A report of 60 nmol/L is 25.5 µg/L of the diphosphate, but 15.9 µg/L if the free-thiamine factor is used — a difference large enough to change which side of a laboratory's µg/L cut-off the result falls on
Two molecular weights, and why only one of them belongs here
| Form | Molecular weight | Factor, µg/L → nmol/L | 50 µg/L becomes |
|---|---|---|---|
| Thiamine diphosphate (TDP, TPP) — the coenzyme, and what whole-blood assays measure | 425.31 | × 2.35123 | 117.6 nmol/L |
| Free thiamine — the unphosphorylated vitamin | 265.35 | × 3.76865 | 188.4 nmol/L |
| Ratio between them | 1.603 | 1.603 | 60% higher, for the same blood |
Specimen handling, and what it does to the result
| Requirement | Why | What happens if it is missed |
|---|---|---|
| Whole blood, EDTA — not serum or plasma | About 80% of blood thiamine is intracellular, held in red cells as the diphosphate | A serum or plasma thiamine measures the small free fraction and is close to meaningless as a measure of status |
| Protect from light, amber tube | Thiamine is photolabile | The measured concentration falls, and a normal result can be reported as low |
| Separate and freeze promptly | Mayo require the specimen light-protected and frozen; stability is quoted as 28 days that way | Delayed or warm transport lowers the result |
| Draw before treatment, not after | Parenteral thiamine raises the blood level within minutes | A post-treatment level is uninterpretable, and a sample drawn after the first dose cannot be used to argue the patient was never deficient |
When thiamine is suspected, the level never gates treatment
| Situation | What to do | Where the level fits |
|---|---|---|
| Suspected Wernicke’s encephalopathy | Give parenteral thiamine immediately, on suspicion | Draw the sample before the first dose if that costs no time — then treat without waiting for it |
| Alcohol-use disorder, admission or withdrawal | Parenteral thiamine before any carbohydrate load | Rarely needed; treatment is empirical |
| Refeeding after prolonged starvation, bariatric surgery, hyperemesis, prolonged parenteral nutrition | Thiamine before and during refeeding | A level may document the deficiency but does not decide the treatment |
| Unexplained high-anion-gap lactic acidosis or heart failure not responding to usual measures | Consider a thiamine trial | A level drawn at the same time may be informative in retrospect |
The coenzyme, the specimen and the emergency
Whole-blood thiamine is reported either as a mass concentration — micrograms per litre, identical to nanograms per millilitre — or as an amount of substance in nanomoles per litre. Converting between them needs a molecular weight, and the molecular weight that belongs here is 425.31: thiamine diphosphate, the phosphorylated coenzyme. That is the form held inside red cells, the form bound to transketolase and the dehydrogenase complexes, and the form a whole-blood assay is calibrated against. Free thiamine weighs 265.35, and a conversion factor derived from it is 3.76865 rather than 2.35123 — larger by a factor of 1.603. Published factors for “thiamine” often do not say which species they mean, so a result converted from an unlabelled factor and one converted properly can differ by about 60%. At the top of the interval that is the difference between a normal result and a raised one.
The second thing the page exists to say is about the specimen. Roughly four-fifths of the thiamine in blood is inside the red cells, so the measurement has to be made on whole blood collected into EDTA. A serum or plasma thiamine samples only the small free fraction, moves with the last meal and tells you very little; if a report says serum, the number is not a measure of thiamine status. Thiamine is also photolabile, which is why laboratories ask for an amber tube and prompt freezing. A light-exposed or slowly transported sample gives a falsely low result, and a falsely low thiamine is a diagnosis manufactured by the transport system.
The third point is the one that changes what happens to patients. Where Wernicke’s encephalopathy is suspected — the classical triad of confusion, ophthalmoplegia and ataxia is present in a minority, so suspicion has to be generous — parenteral thiamine is given immediately, on suspicion. The blood level is drawn before treatment if that costs no time, and is then never waited for. In most hospitals the assay is sent away and reported in days; the condition it might confirm causes irreversible Korsakoff’s amnesia within hours if it is left untreated, and thiamine is safe. Glucose given to a thiamine-deplete patient before thiamine can precipitate the encephalopathy, which is why intravenous thiamine precedes any carbohydrate load in alcohol-related presentations and in refeeding.
Read a normal result carefully. A whole-blood thiamine inside the reference interval does not exclude Wernicke’s encephalopathy, and a result drawn after the first dose of treatment cannot be used to argue the patient was never deficient. The test documents; it does not decide.
Frequently asked questions
How do you convert thiamine from µg/L to nmol/L?
Multiply by 2.35123. That factor comes from the molecular weight of thiamine diphosphate, 425.31 g/mol, which is the species a whole-blood assay measures. A thiamine of 50 µg/L is 117.6 nmol/L. To go the other way, divide the nmol/L figure by 2.35123. µg/L and ng/mL are numerically identical, so no conversion is needed between those two.
Why do some conversion factors for thiamine give a different answer?
Because they were derived from free thiamine, molecular weight 265.35, rather than from thiamine diphosphate at 425.31. The free-thiamine factor is 3.76865 nmol/L per µg/L against the correct 2.35123 — a ratio of 1.603. Applied to a whole-blood result it inflates the molar figure by about 60%, which is easily enough to move a mid-normal result above the reference interval.
Can thiamine be measured on serum or plasma?
It can be measured, but it should not be used. About 80% of the thiamine in blood is inside the red cells, held as the diphosphate, so a serum or plasma level reflects only the small free fraction and moves with recent intake. Whole blood collected into EDTA, protected from light, is the specimen that reflects status.
Do you wait for a thiamine level before treating suspected Wernicke's encephalopathy?
No. Parenteral thiamine is given immediately on clinical suspicion. Draw the sample before the first dose if that costs no time, then treat without waiting for the result — the assay is usually a send-away test reported in days, the encephalopathy causes permanent amnesia within hours, and thiamine is safe. A normal level does not exclude the diagnosis, and a level taken after treatment has started cannot be interpreted.
Why does the sample have to be protected from light?
Thiamine is degraded by light, so an unprotected sample loses thiamine between the ward and the analyser and is reported lower than the patient’s true level. Laboratories ask for an amber tube or a foil-wrapped tube and prompt freezing for that reason. A mishandled sample is a common cause of an unexpectedly low thiamine in a patient with no reason to be deficient.
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References
- Galvin R, Bråthen G, Ivashynka A, et al. EFNS guidelines for diagnosis, therapy and prevention of Wernicke encephalopathy. Eur J Neurol. 2010;17(12):1408–1418. doi:10.1111/j.1468-1331.2010.03153.x
- Mayo Clinic Laboratories. Test ID: TDP — Thiamine (Vitamin B1), Whole Blood. Reference values 70–180 nmol/L; values below 70 nmol/L suggestive of deficiency. Whole blood EDTA, 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.
- National Institute for Health and Care Excellence. Alcohol-use disorders: diagnosis and management of physical complications. Clinical guideline CG100. London: NICE; 2010 (updated 2017).
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.