Taking 10 mg/d of biotin for 7 days was associated with falsely increased results from the Roche cobas e602 assay for free T4 (P= .01) and free T3 (P= .005) and from the Siemens Vista Dimension 1500 assay for free T3 (P< .001). A unique color is used for each participant across all panels. The dotted lines represent the lower and the upper reference range for each assay. For prolactin, 2 women were represented by triangles and 4 men by dots. Red dotted lines represent normal range of prolactin for women and black for men. Architect indicates Abbott Architect 2000; Centaur, Siemens Centaur XP; cobas, Roche cobas e602; Vista, Siemens Vista Dimension 1500; and Vitros, OCD Vitros 5600. For SI conversion factors, see the Methods section.