Drugs interfering with the assessment of thyroid function tests.
Principal mechanisms by which drugs can give rise to spurious thyroid test results are as follows:
  1. Assay interference
  2. Changes in levels of serum thyroid binding proteins (TBPs) - particularly thyroid-binding globulin (TBG)
  3. Alteration in affinity or binding of thyroid hormones to serum TBP.
The common medications which modify thyroid test results by the above processes shall be discussed in the following sections.
Drugs causing assay interference
Medications can interfere with the accurate estimation of the thyroid profile due to interference with components of the assays used. Biotin and heparin are commonly used medications that cause TFT abnormalities in euthyroid individuals by distinct mechanisms.