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How to Make Sense of Thyroid Blood Tests

Over the last decade, some doctors have changed how they interpret thyroid blood tests. Certain drugs can throw these laboratory tests off.

As many as 20 million people in the US have thyroid disorders, according to the American Thyroid Association. But how would you know if your thyroid gland is functioning properly or not? First and foremost, doctors rely on thyroid blood tests to determine the health of the gland. Unfortunately, however, they don’t always agree on the correct interpretation of the results.

How Is Your Thyroid Doing?

Q. Since 2011, I have taken levothyroxine for hypothyroidism. I recently had my annual check-up with my family physician, who oversees my thyroid treatment. The lab work showed my TSH was elevated, while my free T4 was in the normal range.

I have noticed for the past few months that my eyebrows are becoming sparser, as well as my pubic hair. My toenails are also extremely brittle.

I am a very active person, yet I have gained 15 pounds since I saw my doctor last year. When my TSH was measured then, it was in the normal range. I wondered if I might need to have my dosage of levothyroxine adjusted, but my doctor said the results are fine.

A Second Opinion Regarding Your Thyroid Blood Tests:

A. You might want a second opinion. An elevated TSH suggests that your thyroid is not fine. In addition, your symptoms of weight gain, brittle nails and eyebrow hair loss are consistent with hypothyroidism. Consequently, you might indeed need to have your dose of levothyroxine adjusted.

Preparing for Your Doctor Visit:

To prepare you for your meeting, we are providing you with our Guide to Thyroid Hormones. This downloadable pdf contains 25 pages of information such as other symptoms of an underactive thyroid gland (depression, fatigue, puffy eyes, elevated cholesterol and more).

The Guide also tells how to interpret laboratory tests for thyroid disease. Endocrinologists have been considering changes to the cutoffs for hypothyroidism, but they do not necessarily agree. (To learn more about this controversy, you may wish to listen to Show 1015: Thyroid Mysteries, Controversies and the Latest Research).

Moreover, the Guide lists some medications that may interfere with thyroid blood tests. Amiodarone, propranolol or tamoxifen could all lead to a falsely elevated value for T4. In your case, that could mask a worsening of your condition suggested by your symptoms and your high level of TSH.

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About the Author
Terry Graedon, PhD, is a medical anthropologist and co-host of The People’s Pharmacy radio show, co-author of The People’s Pharmacy syndicated newspaper columns and numerous books, and co-founder of The People’s Pharmacy website. Terry taught in the Duke University School of Nursing and was an adjunct assistant professor in the Department of Anthropology. She is a Fellow of the Society of Applied Anthropology. Terry is one of the country's leading authorities on the science behind folk remedies..
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