Vitamin H (Biotin B8)

Biotin (vitamin B8, also called vitamin H) is a water-soluble vitamin. It is a helper substance for a group of enzymes (the carboxylases) that are needed to release energy from food and to build fatty acids. Biotin also contributes to maintaining normal skin and normal hair and to the functioning of the nervous system. It is found mainly in eggs, liver, milk, nuts and peanuts, and gut bacteria also make part of it.

• A rare biotin deficiency, for example from eating a lot of raw eggs over a long period
• A high intake from supplements, which matters because biotin can interfere with other laboratory tests
• Rarely: an inborn enzyme deficiency (biotinidase deficiency), which is detected in the Netherlands through the heel prick

With a high value and unexpected other results, the GP usually has those results measured again after the biotin supplement has been stopped for a few days, sometimes on a different analyzer. With a low value and skin, hair or nerve symptoms, the GP looks at eating pattern and at other causes of those symptoms.

As a measure of vitamin status, the test has been little studied and there are no agreed limit values. The result is mainly meaningful when other results do not add up: with an unusual combination of thyroid values, according to the Dutch guideline on thyroid function disorders, interference with the measurement should be considered, and a high biotin level is then a possible explanation. The same guideline states that interference by biotin on the common platforms has largely been resolved since about 2021, but this does not apply to every measurement method.

• Biotin in high doses (hair and nail supplements, some multivitamins) can interfere with other immunoassays, including thyroid tests (TSH and free T4), troponin and various hormones; depending on the method, the result comes out too high or too low. Therefore stop high doses of biotin at least two days before the blood draw.
• The biotin measurement itself is also strongly raised by a supplement; the result then only says something about intake over the last few days.
• Gut bacteria make biotin, so the blood value does not simply reflect intake or stores.
• Measurement methods and reference values differ between laboratories and are not standardized.

A dietary biotin deficiency hardly ever occurs in the Netherlands. The inborn form, biotinidase deficiency, is rare: on average 2 to 4 children a year are born with it, and they are detected through the heel prick and treated immediately. How often a raised value due to supplements occurs is not registered, but biotin is found in many over-the-counter hair and nail supplements.

In adults with a varied diet, the result adds little; a deficiency is rare and hair or nail problems usually have another cause. The test can be useful if other laboratory results are unexpectedly abnormal and there is a suspicion that a biotin supplement is interfering with those results. For newborns, screening for biotinidase deficiency is done through the heel prick, not through this test.

• A high biotin level can distort other results and thus lead to a wrong conclusion, for example about the thyroid.
• A slightly low value can wrongly explain hair or nail problems, so that another cause is found later.

• Voedingscentrum: Biotine (vitamine B8)
• FMS Richtlijnendatabase, richtlijn Schildklierfunctiestoornissen: Biochemische bepalingen
• RIVM, Pre- en neonatale screeningen: De ziekten die de hielprik opspoort
• Thuisarts.nl: Heb ik extra vitamines nodig?