process called biotinylation. the choice of which chemical modification to use is responsible for the biotin reagent binding to a specific protein. second, the sample is incubated with avidin bound to beads, then rinsed, removing all unbound proteins, while leaving only the biotinylated protein bound to avidin. last, the biotinylated protein can be eluted from the beads with excess free biotin. the process can also utilize bacteria-derived streptavidin bound to beads, but because it has a higher dissociation constant than avidin, very harsh conditions are needed to elute the biotinylated protein from the beads, which often will denature the protein of interest. interference with medical laboratory results when people are ingesting high levels of biotin in dietary supplements, a consequence can be clinically significant interference with diagnostic blood tests that use biotin-streptavidin technology. this methodology is commonly used to measure levels of hormones such as thyroid hormones, and other analytes such as 25-hydroxyvitamin d. biotin interference can produce both falsely normal and falsely abnormal results. in the us, biotin as a non-prescription dietary supplement is sold in amounts of 1 to 10 mg per serving, with claims for supporting hair and nail health, and as 300 mg per day as a possibly effective treatment for multiple sclerosis (see § research). overconsumption of 5 mg/day or higher causes elevated concentration in plasma that interferes with biotin-streptavidin immunoassays in an unpredictable manner. healthcare professionals are advised to instruct patients to stop taking biotin supplements for 48 h or even up to weeks before the test, depending on the specific test, dose, and frequency of biotin uptake. guidance for laboratory staff is proposed to detect and manage biotin interference. history further information: vitamin § history in 1916, w. g. bateman observed that a diet high in raw egg whites caused toxic symptoms in dogs, cats, rabbits, and humans. by 1927, scientists such as margarete boas and helen parsons had performed experiments demonstrating the symptoms associated with "egg-white injury." they had found that rats fed large amounts of egg-white as their only protein source exhibited neurological dysfunction, hair loss, dermatitis, and eventually, death. in 1936, fritz kögl and benno tönnis documented isolating a yeast growth factor in a journal article titled "darstellung von krystallisiertem biotin aus eigelb." (representation of crystallized biotin from egg yolk). the name biotin derives from the greek word bios ('to live') and the suffix "-in" (a general chemical suffix used in organic chemistry). other research groups, working independently, had isolated the same compound under different names. hungarian scientist paul gyorgy began investigating the factor responsible for egg-white injury in 1933 and in 1939, was successful identifying what he called "vitamin h" (the h represents haar und haut, german for 'hair and skin'). further chemical characterization of vitamin h revealed that it was water-soluble and present in high amounts in the liver. after experiments performed with yeast and rhizobium trifolii, west and wilson isolated a compound they called co-enzyme r. by 1940, it was recognized that all three compounds were identical and were collectively given the name: biotin. gyorgy continued his work on biotin and in 1941 published a paper demonstrating that egg-white injury was caused by the binding of biotin by avidin. unlike for many vitamins, there is insufficient information to establish a recommended dietary allowance, so dietary guidelines identify an "adequate intake" based on best available science with the understanding that at some later date this will be replaced by more exact information. using e. coli, a biosynthesis pathway was proposed by rolfe and eisenberg in 1968. the initial step was described as a condensation of pimelyl-coa and alanine to form 7-oxo-8-aminopelargonic acid. from there, they described three-step process, the last being introducing a sulfur atom to form the tetrahydrothiophene ring. research multiple sclerosis high-dose biotin (300 mg/day = 10,000 times adequate intake) has been used in clinical trials for treatment of multiple sclerosis, a demyelinating autoimmune disease. the hypothesis is that biotin may promote remyelination of the myelin sheath of nerve cells, slowing or even reversing neurodegeneration. the proposed mechanisms are that biotin activates acetyl-coa carboxylase, which is a key rate-limiting enzyme during the synthesis of myelin, and by reducing axonal hypoxia through enhanced energy production. clinical trial results are mixed; a 2019 review concluded that a further investigation of the association between multiple sclerosis symptoms and biotin should be undertaken, whereas two 2020 reviews of a larger number of clinical trials reported no consistent evidence for benefits, and some evidence for increased disease activity and higher risk of relapse. hair, nails, skin in the united states, biotin is promoted as a dietary supplement for strengthening hair and fingernails, though scientific data supporting these outcomes in humans are very weak. a review of the fingernails literature reported brittle nail improvement as evidence from two pre-1990 clinical trials that had administered an oral dietary supplement of 2.5 mg/day for several months, without a placebo control comparison group. there is no more recent clinical trial literature. a review of biotin as treatment for hair loss identified case studies of infants and young children with genetic defect biotin deficiency having improved hair growth after supplementation, but went on to report that "there have been no randomized, controlled trials to prove efficacy of supplementation with biotin in normal, healthy individuals." biotin is also incorporated into topical hair and skin products with similar claims. the dietary supplement health and education act of 1994 states that the us food and drug administration must allow on the product label what are described as "structure:function" (s:f) health claims that ingredient(s) are essential for health. for example: biotin helps maintain healthy skin, hair and nails. if a s:f claim is made, the label must include the disclaimer "this statement has not been evaluated by the food and drug administration. this product is not intended to diagnose, treat, cure, or prevent any disease." animals in cattle, biotin is necessary for hoof health. lameness due to hoof problems is common, with herd prevalence estimated at 10 to 35%. consequences of lameness include less food consumption, lower milk production, and increased veterinary treatment costs. results after 4–6 months from supplementing biotin at 20 mg/day into daily diet reduces the risk of lameness. a review of controlled trials reported that supplementation at 20 mg/day increased milk yield by 4.8%. the discussion speculated that this could be an indirect consequence of improved hoof health or a direct effect on milk production. for horses, conditions such as chronic laminitis, cracked hooves, or dry, brittle feet incapable of holding shoes are a common problem. biotin is a popular nutritional supplement. there are recommendations that horses need 15 to 25 mg/day. studies report biotin improves the growth of new hoof horn rather than improving the status of existing hoof, so months of supplementation are needed for the hoof wall to be completely replaced.