[Chronic kidney failure and biotin: A combination inducing unusual results in thyroid and parathyroid investigations, report of 2 cases].

In clinical chemistry, many immunoassays apply biotin and streptavidin in the assay principle. Presence of high levels of biotin in patient samples can produce negative or positive interference depending on the assay format. In this study, we describe 2 clinical cases with chronic kidney failure and with unusual thyroid and parathyroid function test results due to biotin interference. We studied the impact of biotin levels on thyroid stimulating hormone (TSH), free thyroxine (T4L) and parathormone (PTH) results with a pool of sera loaded with several concentrations of biotin. In sandwich assays (TSH and PTH), excess biotin displaces biotinylated antibodies resulting in apparently low concentration of the analyte. With competitive immunoassays (T4L), excess biotin competes with biotinylated analog for the binding sites on streptavidin resulting in low signal and falsely high concentration of the analyte. In conclusion, chronic kidney failure combined to therapeutic biotin is in favour of high levels of biotin which causes seriously misleading results in assays using biotin-streptavidin mechanisms.