First-generation TSH assays were done by radioimmunoassay and were introduced in 1965.[1] There were variations and improvements upon TSH radioimmunoassay, but their use declined as a new immunometric assay technique became available in the middle of the 1980s.[3][2] The new techniques were more accurate, leading to the second, third, and even fourth generations of TSH assay, with each generation possessing ten times greater functional sensitivity than the last.[7] Third generation immunometric assay methods are typically automated.[3] Fourth generation TSH immunometric assay has been developed for use in research.[4]