Endocrine Abstracts

Introduction: Biotin (vitamin B8) is a coenzyme of carboxylases involved in many metabolic pathways and also used in therapeutics as a dietary supplement (diffuse alopecia)(<30 mg/day), in the treatment of rare congenital enzymatic deficiencies (5–40 mg/day) or more recently in the treatment of progressive multiple sclerosis at higher doses (300 mg/day). At such high doses, interferences with thyroid hormones assays using biotin-streptavidin amplification system were reported, leading to an apparent biological hyperthyroidism (low T4L, high TSH) (Piketty, 2000).

Materials and methods: The impact of biotin concentrations ranging from 5 to 400 ng/ml, thus covering the range of serum levels reached in therapeutics, was evaluated on a wide panel of serum hormones (TSH, T4L, T3L, Tg, FSH, LH, SHBG, Prolactin, estradiol, progesterone, and cortisol), assayed on the automated analyzer (Cobas^®, Roche).

Results: We confirmed that TSH, T4L and T3L were the most sensitive parameters to biotin interference, being significantly affected from a biotin concentration of 30 mg/l (induced variation superior to the accepted inacurrancy of these assays, i.e. 5–10%). Thyroid parameters were followed by steroids (estradiol, progesterone, and cortisol) and FSH which were affected from a biotin concentration of 40 mg/l, and finally by the other protein hormones (LH, SHBG, Prolactin, and Tg) affected from a biotin concentration of 80 mg/l. Interestingly, biotin interference depended particularly on the ratio between the volumes of patient serum and of biotin-streptavidin reagent required for the dosage.

Conclusion: Below a biotin concentration of 30 mg/l, only thyroid parameters seem to be affected. Therefore, in patients treated by high doses of biotin for multiple sclerosis, hormones should be either dosed on an analyzer, not using biotin-streptavidin amplification system or assayed after specific pre-treatment of blood samples . For other biotin-based treatments at lower dose, the respect of a minimal delay after biotin ingestion before blood sampling should prevent from any significant interference (8h for 10 mg, 3h for 5 mg).