Biotin supplements and laboratory test results in neuropsychiatric practice and research

Biotin is a water-soluble B group vitamin, also known as Vitamin B7 or Vitamin H. Biotin is a cofactor for carboxylating enzymes. Patients who are seen in neuropsychiatric or medical practice may take biotin supplements to treat hair loss associated with valproate treatment,[1,2] for hair loss due to other conditions,[3] for other dermatological conditions,[3] for multiple sclerosis,[4] for other neurological disorders such as biotin-thiamine-responsive basal ganglia disease,[5] for other health-related indications,[6] or merely as an included vitamin in over-the-counter supplements that are intended to promote health and well-being; such supplements may contain biotin even when the label does not say so.[7]

Biotin in such supplements has long been recognized to interfere with certain immunoassays. For example, Waghray et al.[8] reported that 2 patients who were taking biotin (1.5 mg/day and 5 mg/day) had surprisingly low parathyroid hormone levels; the role of biotin interference in the assay was confirmed in one patient when the patient was retested after discontinuing biotin. Many other and even far earlier reports have been published.[9]

BIOTIN INTERFERENCE: MECHANISM

Why do biotin supplements interfere with immunoassays? Biotin is a small molecule which, when conjugated with biologically active macromolecules (such as an antibody to the target of an assay), rarely interferes with the function of the labeled molecule. Streptavidin is a glycoprotein that has a very high affinity for biotin; the binding is highly specific, is resistant to changes in temperature and pH, and can withstand the presence of denaturing agents and organic solvents. By attaching the streptavidin protein to a moiety such as a fluorophore, an enzyme, or a gold nanoparticle, the streptavidin-biotin interaction can serve as a detection method in a wide range of laboratory applications such as enzyme-linked immunosorbent assays (ELISA), chemiluminescence immunoassays (CLIA), western blotting, and flow cytometry, among others. ELISA and CLIA are routinely used in clinical biochemistry laboratories to assay hormones, vitamins, therapeutic drugs, tumor markers, and other targets.

Biotin interference can occur in immunoassays that employ streptavidin-biotinylated antibodies when high biotin levels in blood samples, resulting from the use of oral biotin supplements, interfere with the streptavidin-biotin binding, thus distorting signal detection in these tests.

BIOTIN INTERFERENCE: EVIDENCE

Li et al.[10] examined the performance of specific biotinylated immunoassays in a nonrandomized crossover trial conducted in 6 healthy adults who received supplementation with oral biotin. The mean age of the sample was 38 years. The sample was 33% female. No participant was receiving nutritional supplements. These participants were administered oral biotin in the dose of 10 mg/day for 1 week. Whereas this dose is very high, being >300 times the daily intake guidance,[10] it was chosen because it is common in over-the-counter supplements, and because doses of 10 mg/day and higher are common when biotin is prescribed in dermatological, medical, or neuropsychiatric conditions.

Li et al.[10] assayed the levels of 9 hormones and 2 nonhormones in blood 2 h after dosing on the last day of biotin treatment and again, a week later, in a biotin-free state; these hormonal and nonhormonal targets were thyroid-stimulating hormone, total thyroxine, total triiodothyronine, free thyroxine, free triiodothyronine, parathyroid hormone, prolactin, N-terminal pro-brain natriuretic peptide, 25-hydroxyvitamin D, prostate-specific antigen, and ferritin.

There were 37 immunoassays run: 23 that had biotin and streptavidin components and 14 that had not; the latter were negative controls. Important findings from the study are presented in Box 1. In summary, the study showed that nearly 40% of persons who take biotin supplements (10 mg/day) may receive reports of falsely high or falsely low values on a variety of hormonal or biochemical tests that are based on commonly used biotinylated immunoassays.

Box 1.

Effect of biotin 10 mg/day on immunoassay results*

Of note, this study[10] was conducted in healthy adults. Similar investigations need to be conducted in disorder-specific patient samples to estimate the risk of abnormal assay outcomes with different types of assays; however, preliminary data for some assays in some disorders already exist. it is also important to know at what biotin doses for what assays the biotin interference becomes clinically relevant and for how long after the last biotin dose the interference persists. In their discussion, Li et al.[10] considered a large number of sources of variation in the magnitude of the biotin interference, and important possibility that emerged is that higher doses and longer durations of treatment could be associated with longer durations of interference after biotin discontinuation.

In support of the results of Li et al.,[10] Ali et al.[11] also examined biotin interference in immunoassays of a range of targets; prominent fallacious results were identified for prolactin and thyroid-stimulating hormone, among others.

TAKE-HOME MESSAGE

Besides clinical practice, biotinylated assays are also used in research, such as for the estimation of levels of cytokines in studies of inflammatory mechanisms in depression, schizophrenia, and Alzheimer's disease. The take-home message, therefore, is that clinicians and researchers who order blood levels of vitamins such as Vitamin D, Vitamin B12, and folate, hormones such as thyroid hormones and thyroid-stimulating hormone, or other substances should also enquire about additional medications, including supplements, that the patient may be taking; should biotin supplementation be identified, this should be communicated to the laboratory that performs the tests. Should biotin interference be deemed likely, blood draw for the test should be deferred until after discontinuation of biotin for at least 3–7 days.[10]