Thyroid function testing and automation

Automation of thyroid hormone testing has been advanced by the use of chemiluminescence as a signal generation system. Enzyme immunoassays that use colorimetry or fluorescence generally lack the sensitivity of chemiluminescence, can be matrix sensitive, and are limited by interference from background fluorescence and quenching effects. The measurement of thyroid stimulating hormone (TSH) is a prime example of the advantages that chemiluminescence brings to the automation of thyroid testing. Until the development of chemiluminescence, most sensitive TSH immunoassays lacked the ability to measure TSH below 0.1 μU/mL because of poor precision. This compromised the use of this assay to discriminate low normal from a suppressed TSH level found in patients with hyperthyroidism. Chemiluminescence brings to automation the ability to reach levels of TSH that can accurately and precisely discriminate low normal from a true suppressed level. Chemiluminescence as a signal generating technology has now been brought to a new level of sensitivity by the use of added chemicals that enhance the luminescent signal more than 1,000 fold. Enhanced chemiluminescence has the ability to reach a minimum detection limit of 10^{- 20} moles of tracer which far exceeds the detection limits needed for a true ultra-sensitive TSH assay. Automated systems that employ enhanced chemiluminescence have a decided advantage in reaching the detection limits needed for the measurement of thyroid hormones.