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The page below is a sample from the LabCE course Laboratory Assessment of Thyroid Function. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Analytical Methods for Thyroid Hormone Measurement

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.




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.