TRH and hyperthyroidism: A high-sensitive fourth generation TSH assay, which has a functional sensitivity of 0.001 μIU/mL, could predict the results of the TSH fold-response upon TRH stimulation, which is used to evaluate subclinical hyperthyroidism, leading to elimination of the TRH stimulation test, which causes side effects, such as nausea (Spencer et al., 1993).