Laboratory analysis of the thyroid hormones and thyroid function tests span the range of analytical principles. Most clinical laboratories with an automated immunoassay system offer a menu of free T4, free T3 and thyroid-stimulating hormone (TSH), with a smaller number offering thyroid autoantibody testing.
Principle
|
Comments
|
Spectrophotometric
|
Historical methods for the analysis of total T4 and T3 employed sprectrophotometric principles, some of which were automated on general chemistry analyzers for high-throughput screening. |
Radioimmunoassay (RIA)
|
Many of the first automated thyroid hormone assays and TSH methods employed RIA. Now, less frequently used, with the exception of reverse T3 assays. |
Enzyme-linked immunosorbent assay (ELISA)
|
ELISA principles dominate the manual microplate assays, which are used less frequently in laboratories with an automated immunoassay system. |
Fluorescence polarization immunoassay (FPIA)
|
Once a fairly commonly used principle in laboratories transitioning from RIA methods, less commonly used today. |
Chemiluminescence immunoassay (CIA)
|
One of the most commonly used principles in automated immunoassay systems, providing enhanced sensitivity and precision |
High-performance liquid chromatography (HPLC) and LC-mass-spectrometry (LC-MS)
|
Chromatographic methods typically have the highest achievable degree of sensitivity and are free from non-specific interferences with heterophile antibodies. Not widely used in small-to-mid-size laboratories. |
On the pages to follow, a more detailed overview is provided on the laboratory analysis of the thyroid markers.