Thyroid blood tests are an important part of diagnosing and treating thyroid disease.
The results can be difficult to understand because the diagnosis can change based on the relationship of values.
Different combinations of values can mean different things, and there is often more than one meaning.
Verywell
When you have thyroid disease, your thyroid gland produces too little or too much of a hormone.
It acts as a chemical messenger, telling the thyroid gland when to start producing thyroid hormones.
When thyroid hormone levels are low, more TSH is produced to stimulate production.
Get our printable guide for your next healthcare provider’s appointment to help you ask the right questions.
When levels are normal, the pituitary gland stops producing TSH.
The TSH test measures how much or how little TSH there is in the bloodstream.
Triiodothyronine (T3)
Triiodothyronine(T3) is the active thyroid hormone converted from T4.
As with T4, there is both bound and free T3.
T3 blood tests include:
Is T3 or T4 More Important?
T4 is generally the more important thyroid hormone to measure.
Thyroglobulin (Tg)
Thyroglobulin(Tg) is a protein made by the thyroid gland.
It’s mostly used to help guide the treatment ofthyroid cancer.
A high Tg level is a sign that cancer cells are still present after these treatments.
It can also tell them if the cancer is inremission.
Thyroid Antibodies
Some thyroid diseases like Hashimoto’s thyroiditis and Graves' disease areautoimmune disorders.
These are diseases in which the immune system targets and attacks normal thyroid cells.
They can help determine the cause of a thyroid problem if your thyroid gland is functioning normally.
What Results Mean
The results of thyroid blood tests are described in a reference range of values.
The reference range has a high and low value between which results are considered normal.
Values near the upper or lower limit are borderline, while anything outside of these limits is considered abnormal.
Reference ranges and units can vary from lab to lab.
To ensure consistency in your test results, use the same lab for every test.
Get our printable guide for your next healthcare provider’s appointment to help you ask the right questions.
TSH Interpretations
On its own, the TSH test can diagnose thyroid disease, albeit with limitations.
Other Interpretations
Other thyroid tests may be included in the workup.
Some have specific aims, while others are used for screening purposes or to evidence possible causes.
The combined results can paint a clearer picture of the cause of thyroid disease.
The tests can also monitor how effective thyroid treatments are, including the treatment of thyroid cancer.
Society for Endocrinology: You and Your Hormones.Thyroid gland.
American Thyroid Association.Hypothyroidism (underactive).
American Thyroid Association.Hyperthyroidism (overactive).
Colorado State University: VIVO Pathophysiology.Chemistry of thyroid hormones.
Indrasena BS.Use of thyroglobulin as a tumour marker.World J Biol Chem.
2015;100(5):E799-E807.
2023;15(6):e40140.
2021;5(6):bvab042.
2018;34(4S Suppl 1):S13-S19.
2024;10(4):e26092.
Published 2017 May 9. doi:10.3389/fimmu.2017.00521
MedlinePlus.What you’re gonna wanna know about blood testing.
University of California, Los Angeles: UCLA Health.What are normal thyroid hormone levels?
American Thyroid Association.Subclinical Thyroid Disease.
2014;24(12):1670-1751. doi:10.1089/thy.2014.0028
American Thyroid Association.Thyroid Function Tests.
Cancer Therapy Advisor.Sick-euthyroid syndrome.
Garber J, Cobin R, Gharib H, et.
2012;18(6).
2013;27(5):701-712. doi:10.1016/j.beem.2013.07.003
