Section 862.1685 - Thyroxine-binding globulin test system(a)Identification. A thyroxine-binding globulin test system is a device intended to measure thyroxine (thyroid)-binding globulin (TBG), a plasma protein which binds thyroxine, in serum and plasma. Measurements obtained by this device are used in the diagnosis and treatment of thyroid diseases.(b)Classification. Class II (special controls). The device is exempt from the premarket notification procedures in subpart E of part 807 of this chapter subject to the limitations in § 862.9 .52 FR 16122, May 1, 1987, as amended at 84 FR 71797 , Dec. 30, 2019