Biotin (Vitamin B7)

The direction rule is settled; the amount of biotin needed to trigger it is not. That threshold differs by manufacturer, by test and by how recent the reagent is, and cannot be predicted from one analyser to another. The panel study behind it added biotin to pooled serum in a laboratory rather than measuring people who had swallowed any.

This is a reference chapter, and it reports no incidence figure. The high doses used here treat a specific inherited fault in recycling biotin, and say nothing about biotin in people who do not have it. Reading across from this condition to general supplementation is precisely the error its existence invites. This reflects the chapter as it stood in December 2025.

A clinical reference chapter rather than primary research: it synthesises rather than measures, and puts no number on how rare rare is. The at-risk list is qualitative, with no estimate of how much any of those exposures raises the risk. These chapters are revised continuously, and this reflects the text as it stood in September 2025.

The dose figures are what the agency was aware of in 2019, not a survey of what is on shelves now. The 0.03mg intake figure is itself extrapolated from the biotin content of human milk rather than measured against a requirement, and no Recommended Dietary Allowance was ever set, for lack of evidence.

The table names devices the agency judged had not addressed the risk, and puts no number on the size of the error on any of them. Several entries are point-of-care strip tests rather than the laboratory analysers most hospitals run, and some clearances date to the 1990s. The page carries no version marker, so the count of fourteen is a snapshot of one day in September 2026.

These are case reports, the weakest design there is: uncontrolled, unblinded and uniformly positive, which is the pattern publication bias produces. No randomised trial appeared in the search at all. The conditions involved are individually rare, so the group in which biotin did help is very small.

Three studies is a very thin base, and the review is limited by that rather than by its method: PubMed only, no registration, no pooled estimate. What it found is an absence of demonstrated benefit in people who are not deficient, which is not the same as demonstrated absence of benefit. The authors are practising dermatologists writing about a supplement their patients ask for.

23 samples, and the exposure is multiple sclerosis treatment at doses far above any hair supplement, so the blood levels here are an upper bound rather than what a shopper reaches. Two authors worked for the company developing that high-dose product, which had a commercial interest in characterising this interference. Roche assays only, and the removal step is not perfectly neutral: it shifts parathyroid hormone by about 8%.

Absence of reported harm is not demonstrated safety; it is what an unset upper limit actually means, and the panel that could not set one said so. That panel was writing in 2012 about intravenous nutrition products, before the interference literature existed, and is silent on blood tests.

A single case, paired with a review of other single cases: this shows that something can happen, never how often. The interference was inferred from how fast the results normalised rather than by measuring biotin in the sample. Assay formulations from 2016 have since been revised for biotin tolerance, and this patient's own dose is not a market-typical exposure.

Nobody in this study was misdiagnosed; what was measured was the assay, not a patient outcome. Only three assays were tested, so it cannot say what any particular hospital runs. Whether interference of this size changes a decision depends on where a person's true troponin sits relative to the cut-off, which the design does not test.

Nobody in this experiment had swallowed any biotin; it was added to plasma in a laboratory, and added biotin may not behave quite like biotin absorbed alongside its own breakdown products. The two highest concentrations tested sit far above what ordinary supplement users have been shown to carry. What was measured was the size of the error, not a missed diagnosis.

Voluntary adverse-event reporting shows that something can happen, never how often. The death report carries no published clinical workup, so nothing in it rules out another cause. The agency's figures describe what it was aware of in 2019, in the United States, where assay availability and reagent generations have both moved on since.

Being above the threshold is not the same as a test actually failing, and none of the three reports a wrong result or a harmed patient. All three read exposure off leftover samples or medical records rather than asking people directly, which undercounts a vitamin that is often an unadvertised ingredient in a beauty product. The UK samples were anonymised, with no record of who those patients were or what they were taking.

There is no single rate of people carrying enough biotin to skew a blood test. Three studies using one threshold disagreed widely, and the gap tracks who was sampled and where, so a clean result may only mean few there take supplements.

78 patients in one Taiwanese hospital, and the tolerance figures come from spiking reagents rather than from those patients. Comparing two manufacturers in a single laboratory does not establish a general ranking between them. The highest patient level found was about 3 nanograms per millilitre, so this shows the reagents have improved rather than that these patients were ever at risk.

Most of what is known about biotin skewing blood tests was measured on older reagents. Newer ones tolerate far more, but troponin, the heart-attack test, was not checked, so whether the problem has shrunk depends on a lab's kit.

This is the figure for all six interference types together, and the review does not break it down by cause, so it is not a biotin rate. The 150 patients come from published case reports, which select for cases that went wrong; how many people had an interference and came to no harm is unknowable from this design. It is not a probability that any given biotin user will be misdiagnosed.

The 48 hour figure is the review authors' inference from biotin's half-life, and no study they cite establishes that it clears interference at any dose. It also cannot help the people most exposed: someone arriving at an emergency department has no notice, and people taking biotin for biotinidase deficiency, a mitochondrial disorder or multiple sclerosis cannot stop.

Stopping biotin more than 48 hours before a blood test is advice reasoned from how fast the body clears it. No study has tested the interval, and the US regulator says there is not enough information to know if any stop works.