Section 862.1375 - Histidine test system(a)Identification. A histidine test system is a device intended to measure free histidine (an amino acid) in plasma and urine. Histidine measurements are used in the diagnosis and treatment of hereditary histidinemia characterized by excess histidine in the blood and urine often resulting in mental retardation and disordered speech development.(b)Classification. Class I (general controls). The device is exempt from the premarket notification procedures in subpart E of part 807 of this chapter subject to § 862.9 .52 FR 16122, May 1, 1987, as amended at 65 FR 2306 , Jan. 14, 2000