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LabCorp.com states that high dose biotin will interfere with the commonly used B12 assay which utilizes biotin/streptavidin binding to quantify the B12. They refer to "high dose" as being over 5 mg/day of biotin and recommend an 8 hour wash-out period before the blood draw for the B12 test. With the 300 mg dose that's now being used by MS patients, a longer wash-out period will likely be of benefit prior to B12 testing. Note that other lab tests also use biotin/streptavidin so check with your doctor first if you're having lab work done.

LabCorp.com wrote:In patients receiving therapy with high biotin doses (ie, >5 mg/day), no sample should be taken until at least eight hours after the last biotin administration.

According to LabCorp, high dose biotin will also interfere with both the serum and red blood cell (RBC) folate test. They recommend waiting at least 8 hours after the last dose of biotin prior to folate testing for biotin doses >5 mg/day. Again, doses of 300 mg/day of biotin may require a longer wash-out period.