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
Total T3 – especially useful in combination with rT3 to diagnose reverse T3 syndrome – T3 to rT3 ratio should be about 10:1
Thyroid Antibodies
- Anti-Thyroid Peroxidase (TPO), aka Anti-Microsomal Antibody (+ in >80% of Grave’s and Hashimoto’s patients)
- Anti-Thyroglobulin Antibody (Tg Ab) (+ in >50% of Grave’s and Hashimoto’s patients)
- Anti-Thyroid Stimulating Immunoglobulin (TSI) (+ in about 90% of Grave’s and 10% of Hashimoto’s patients)
- Anti-Thyroid Receptor Antibody (TRAb)
| Antibody | Target | Conditions | Primary Use |
|---|---|---|---|
| Thyroglobulin Antibody (TgAb) | Thyroglobulin protein | Hashimoto’s, Graves’, thyroid cancer | Autoimmunity detection, cancer monitoring (with Tg). |
| Thyroid Peroxidase Antibody (TPOAb) | Thyroid peroxidase enzyme | Hashimoto’s (primary marker), Graves’ | Most sensitive marker for autoimmune thyroid disease. |
| Thyroid-Stimulating Immunoglobulin (TSI) | TSH receptor | Graves’ disease | Specific for diagnosing Graves’ disease. |
| Thyrotropin Receptor Antibody (TRAb) | TSH receptor | Graves’, Hashimoto’s | Broader marker for thyroid receptor activity. |
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
