Thyroid tests are misunderstood by patients and doctors alike.  Here is a run down of the various options for thyroid testing.  We typically run the basic thyroid panel and/or thyroid antibodies panel.  The less helpful / more specific tests are not that useful and/or reserved for monitoring thyroid cancer, etc.

Basic Thyroid Panel

Thyroid Stimulating Hormone (TSH) – the pituitary hormone released to increase thyroid output from the thyroid gland.  Under ideal circumstances, TSH goes up in low thyroid conditions and down (suppressed) in high thyroid conditions.  The serum and brain levels of T4 and T3 will both feedback to the brain and pituitary to regulate TSH output.

Free T4 – the portion of T4 that is not protein bound, and thus “free”, which is the bioactive portion of circulating T4

Free T3 – the portion of T3 that is not protein bound, and thus “free”, which is the bioactive portion of circulating T3

Reverse T3 – the chemical mirror image of T3, which will bind to thyroid receptors but not activate them, and if present in excess may cause a low thyroid condition caused Reverse T3 Syndrome

Thyroid Antibodies

Thyroid Peroxidase (TPO), present in Hashimoto’s thyroiditis

Thyroglobulin Antibody (Th Ab), present in Hashimoto’s thyroiditis or Grave’s Disease

Thyroid Stimulating Immunoglobulin (TSI), present in Grave’s Disease

Less helpful / more specific thyroid tests

Total T4

Total T3

T3 resin uptake (T3RU)

Free Thyroxin Index (FTI)

Thyroglobulin – protein made only by thyroid cells.  Used to monitor thyroid cancer recurrence

Thyroxine Binding Globulin (TBG), the principal carrier protein for thyroid hormone

Thyroid Stimulating Hormone Receptor Antibody (TRAb), present in autoimmune thyroid disease