Lab Tests Explained: Thyroid Tests

By John Aase • October 7, 2022

As we continue our series on lab tests, Dr. Dave Strobel gives a brief overview of four tests used to gauge thyroid function: TSH, T4, T3, and reverse T3.

He also outlines the normal and optimal ranges for each.

Dr. Strobel's overview on thyroid tests

Thyroid hormones in the body play a significant role in metabolism and growth.

As Dr. Strobel mentioned in our recent video, the normal ranges of blood tests can often be distorted when people who have a disease are included in the supposedly healthy population used to determine those ranges.

Thyroid conditions are a great example of this as they can often be subtler, and therefore go undiagnosed for long periods of time. The optimal range for thyroid tests is really only at one end, or sometimes even slightly outside of, the normal range.

  • Thyroid stimulating hormone, or TSH, is the most commonly performed thyroid test. The normal range is about 0.45–4.5, but the optimal range is in the lower end, or even a little bit below it, at around 0.3–1.5.
  • T4, an inactive thyroid hormone, has its normal range at around 0.8–1.8, but with an optimal range at the upper end, about 1.4–1.8.
  • T3 is the active form of thyroid hormone, and its normal range is about 2.0–4.4, but once again, the optimal range is in the upper part of that range at 3.2–4.4.
  • Reverse T3 is an inactivated form. The normal range is usually around 9.0–25.0, but for the healthy, less than 15 is a good target.

If you are interested in a more in-depth look at these blood tests, including factors that tend to affect test results, check out the Thyroid Tests lesson in the Lab Tests learning module on our website.

HELPcare Clinic membership includes these four thyroid tests, as well as more than 55 others, at no extra charge. The savings are significant. And unhurried primary care appointments at HELPcare Clinic give you and your provider time to dig into the results to better understand what's going on with your health.

Note: These videos are presented for educational purposes only. Your use of this site does not create a doctor-patient relationship. Specific medical advice is only offered through membership in HELPcare Clinic.

John Aase

John is part of HELPcare’s content development team and lives with his wife Bella in Plymouth, Minnesota. He is an MFA candidate at Hamline University.
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