Laboratory analysis of thyroid hormones and thyroid function tests span the range of analytical principles, summarized in Table 9. 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.
Table 9. Analytical Methods for Thyroid Measurement.| Principle | Comments |
| Spectrophotometric | Historical methods for the analysis of total T4 and T3 employed spectrophotometric 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 widely 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. |
The following pages provide a more detailed overview of the laboratory analysis of thyroid markers.
