Biotin (Vitamin B7) Unit Converter
Biotin (Vitamin B7) Unit Converter
Convert serum biotin between ng/mL, µg/L, nmol/L and pmol/L — and understand the reason the test exists: high-dose biotin interferes with biotin-streptavidin immunoassays, reading falsely high on competitive assays and falsely low on sandwich assays.
Biotin (Vitamin B7) converter
Mass ⇄ molarSerum biotin 30 ng/mL, two hours after a 10 mg supplement
The conversion
ng/mL = nmol/L ÷ 4.09316
because 4.09316 = 1 ng/mL ÷ 244.31 g/mol, the molecular weight of biotin
- ng/mL = µg/L
- identical concentrations written two ways; no arithmetic is needed between them
- MW 244.31
- biotin, vitamin B7, C₁₀H₁₆N₂O₃S. A small molecule — which is precisely why it is used as a tag in immunoassay design, and why free biotin from a supplement competes with the tagged reagents
- pmol/L
- a thousandfold smaller than nmol/L, and the unit some endocrine laboratories use. A biotin of 30 ng/mL is 122.79 nmol/L or 122,795 pmol/L
- the concentrations that matter
- an unsupplemented adult usually sits below 0.3 ng/mL. A 10 mg supplement can put the serum concentration into the tens of nanograms per millilitre within one to two hours, and the 100–300 mg daily doses used in multiple sclerosis trials go far higher. Interference thresholds for most affected assays lie in the low tens of ng/mL
Worked example
Serum biotin 30 ng/mL, two hours after a 10 mg supplement
30 ng/mL = 30.00 µg/L — the same number
30 × 4.09316 = 122.79 nmol/L, or 122,795 pmol/L
For scale, Mayo report an unsupplemented adult as under 0.3 ng/mL, so this is roughly a hundredfold above the ordinary dietary concentration
That is the point of measuring it. Roche's Elecsys assays are validated to be free of interference up to about 20 ng/mL of biotin; 30 ng/mL is above that, so any biotin-streptavidin immunoassay run on this sample is suspect
What the interference does depends on the assay design: a competitive assay (free thyroxine, cortisol, many steroids) reads falsely high, and a sandwich assay (TSH, troponin, parathyroid hormone, most tumour markers) reads falsely low
Which way the error goes, and what it looks like on the report
| Assay design | Typical analytes | Direction of error | What it can mimic |
|---|---|---|---|
| Competitive — the analyte competes with a labelled analogue for a limited number of binding sites | Free T4, free T3, total T4, cortisol, testosterone, oestradiol, vitamin D, folate | Falsely HIGH | Thyrotoxicosis; hypercortisolism; androgen excess |
| Sandwich (immunometric) — the analyte is captured between two antibodies | TSH, troponin, parathyroid hormone, hCG, ferritin, prolactin, most tumour markers | Falsely LOW | A missed myocardial infarction; a missed pregnancy; suppressed TSH suggesting thyrotoxicosis |
| The two together | A thyroid panel on one platform | Low TSH with high free T4 | Graves’ disease — the classic biotin pattern, in a patient who is euthyroid |
What a serum biotin result means, and the figures worth knowing
| Concentration | Interpretation |
|---|---|
| Under 0.3 ng/mL | Mayo’s published adult value: consistent with ordinary dietary intake and no supplement. Note this is a one-sided threshold, not a nutritional reference interval |
| Around 10–50 ng/mL | The range reached one to two hours after a single 5–20 mg supplement in volunteer studies. Above most assays’ validated tolerance |
| Hundreds of ng/mL | Seen on the 100–300 mg daily doses trialled in progressive multiple sclerosis, and in some “high-potency” supplement regimens |
| Any low value | Does not diagnose biotin deficiency. Biotinidase deficiency is diagnosed by measuring the enzyme, not the vitamin, and nutritional biotin deficiency is very rare outside prolonged raw-egg-white ingestion, parenteral nutrition without supplementation and some anticonvulsant use |
What to do about it
| Who | Action |
|---|---|
| Patients | Tell the laboratory and the requesting clinician about every supplement containing biotin, including hair, skin and nail products and high-potency B-complex tablets, where doses of 5–10 mg per tablet are common |
| Before a planned blood test | Assay manufacturers commonly advise not sampling until at least 8 hours after the last dose, and longer for high doses. Roche’s Elecsys inserts state that for patients on more than 5 mg/day no sample should be taken until at least 8 hours after the last administration |
| What the FDA actually says | Its 2019 update is more cautious than the 8-hour figure: “sufficient information is not available to know if stopping biotin consumption for any number of hours prior to testing will prevent incorrect test results”. The 8 hours is the manufacturers’ number, not the regulator’s |
| Clinicians | Where a result does not fit the patient, ask about biotin, then ask the laboratory to repeat on a different platform, to dilute, or to strip the biotin before re-assay. A serum biotin can confirm the exposure |
| In suspected myocardial infarction | Do not let a normal troponin reassure you in a patient on high-dose biotin with a convincing history. The FDA’s warning followed a reported death after falsely low troponin results contributed to a missed infarction |
A vitamin nobody is short of, in an assay design almost everybody uses
Biotin, vitamin B7, is reported in nanograms per millilitre — the same number as micrograms per litre — or in nanomoles or picomoles per litre, converting at 4.09316 nanomoles per litre per nanogram per millilitre from a molecular weight of 244.31. The arithmetic is trivial. The reason anyone measures it is not nutritional at all.
Biotin binds streptavidin with an affinity that is among the strongest non-covalent interactions in biology, and immunoassay designers have used that bond for decades to anchor reagents to solid phases. A large share of routine immunoassays on the major automated platforms are built on biotin-streptavidin capture. When a patient has taken a high-dose biotin supplement, the free biotin circulating in their sample competes with the assay’s own biotinylated reagents for those streptavidin binding sites, and the measurement fails — not with an error flag, but with a plausible-looking wrong number.
The direction of the error depends on the assay’s architecture, and both directions are dangerous. In a competitive assay — used for small analytes such as free thyroxine, cortisol and the steroid hormones — excess biotin displaces the labelled tracer from capture, less signal is read, and because signal is inversely related to concentration the result is reported falsely high. In a sandwich, or immunometric, assay — used for larger analytes such as TSH, parathyroid hormone, hCG and the troponins — excess biotin prevents the labelled complex being captured, signal falls, and the result is reported falsely low. Run a thyroid panel on one platform and the two errors combine into a suppressed TSH with a raised free T4: a laboratory picture of Graves’ disease in a euthyroid patient taking a hair-and-nails supplement. Patients have been treated with antithyroid drugs, and in reported cases with radioiodine and surgery, on the strength of it.
The falsely low results are the more lethal. A troponin is a sandwich assay, so biotin pushes it down, and a reassuringly normal troponin in a patient who is actually infarcting is exactly the failure mode that prompted the US Food and Drug Administration’s safety communication in November 2017, updated in November 2019, after a reported patient death. Doses are the reason the problem is common: the daily requirement is around 30 micrograms, over-the-counter hair and nail supplements contain 5 to 10 milligrams and sometimes more, and the regimens trialled in progressive multiple sclerosis reach 100 to 300 milligrams a day. Volunteers given 5 to 20 milligrams reach serum concentrations of tens of nanograms per millilitre within one to two hours, against an unsupplemented value below 0.3. The practical response is to stop biotin before testing — assay manufacturers commonly say at least 8 hours, longer for high doses, while the FDA’s own position is that there is not enough information to be sure any interval is sufficient — and, above all, to tell the laboratory, which can repeat the measurement on a platform that does not use the biotin-streptavidin bond.
Frequently asked questions
How do you convert biotin from ng/mL to nmol/L?
Multiply by 4.09316, which is one nanogram per millilitre divided by biotin’s molecular weight of 244.31 g/mol. A serum biotin of 30 ng/mL is 122.79 nmol/L, or 122,795 pmol/L. Divide by the same factor to go back, and note that ng/mL and µg/L are numerically identical.
How does biotin interfere with blood tests?
Many routine immunoassays use the very strong bond between biotin and streptavidin to anchor their reagents. Free biotin from a supplement competes for those streptavidin binding sites, so the assay misreads the sample. The direction depends on the design: competitive assays, such as free T4 and cortisol, read falsely high, while sandwich assays, such as TSH, parathyroid hormone, hCG and troponin, read falsely low. The result looks entirely plausible — there is no error flag.
Which results should make me suspect biotin interference?
The classic pattern is a suppressed TSH with a raised free T4 in a patient with no clinical thyrotoxicosis — a laboratory picture of Graves’ disease produced by the two errors running in opposite directions on one platform. More dangerous is a falsely low troponin, which can contribute to a missed myocardial infarction; the FDA’s safety communication followed a reported death from exactly that. Any result that does not fit the patient, in someone taking a hair, skin and nail or high-potency B-complex supplement, is worth questioning.
How long should biotin be stopped before a blood test?
Assay manufacturers commonly advise at least 8 hours, and longer for high doses — Roche’s Elecsys inserts state that for patients on more than 5 mg a day no sample should be taken until at least 8 hours after the last dose. The FDA is more cautious: its 2019 update says there is not sufficient information to know whether stopping for any particular number of hours prevents incorrect results. The most reliable step is to tell the laboratory, which can re-assay on a platform that does not use biotin-streptavidin capture.
Why does this page not show a reference interval for biotin?
Because a serum biotin does not grade biotin status. The published adult value is one-sided — under 0.3 ng/mL — and exists to confirm whether enough biotin is present to have interfered with an immunoassay, not to diagnose deficiency. There is no lower bound below which a serum biotin means anything, and biotinidase deficiency is diagnosed by measuring the enzyme, not the vitamin. Printing a normal range under the answer would imply a verdict the test cannot support.
Is a high biotin level harmful in itself?
No toxicity has been established, even at the 100 to 300 milligram daily doses trialled in multiple sclerosis. Biotin is water-soluble and the excess is excreted. The harm is entirely indirect, and entirely in the laboratory: the wrong result, and the treatment or the missed diagnosis that follows from it.
Related calculators
References
- US Food and Drug Administration. UPDATE: The FDA Warns that Biotin May Interfere with Lab Tests — FDA Safety Communication. Original communication 28 November 2017; update 5 November 2019. Reports of falsely low troponin results, including one associated with a patient death.
- Mayo Clinic Laboratories. Test ID: BIOTN — Biotin, Serum. Reference value: 18 years and over, less than 0.3 ng/mL. Liquid chromatography tandem mass spectrometry measuring free biotin.
- Katzman BM, Lueke AJ, Donato LJ, Jaffe AS, Baumann NA. Prevalence of biotin supplement usage in outpatients and plasma biotin concentrations in patients presenting to the emergency department. Clin Biochem. 2018;60:11–16. doi:10.1016/j.clinbiochem.2018.07.004
- Piketty ML, Prie D, Sedel F, et al. High-dose biotin therapy leading to false biochemical endocrine profiles: validation of a simple method to overcome biotin interference. Clin Chem Lab Med. 2017;55(6):817–825. doi:10.1515/cclm-2016-1183
- Bowen R, Benavides R, Colón-Franco JM, et al. Best practices in mitigating the risk of biotin interference with laboratory testing. Clin Biochem. 2019;74:1–11. doi:10.1016/j.clinbiochem.2019.08.012
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.