Why Normal TSH Test Results Don't Always Mean You're OK

What is a TSH Test?

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The ​Thyroid Stimulating Hormone (TSH)  blood test is considered by some physicians to be the only test needed to diagnose and manage an underactive or overactive thyroid, known as hypothyroidism or hyperthyroidism. It is sometimes referred to by conventional endocrinologists as the "gold standard" for diagnosing and treating thyroid conditions.

What Does the TSH Test Measure?

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The TSH test measures the levels of TSH, a hormone that is made and released by your pituitary gland. Your pituitary can sense whether you have enough thyroid hormone in your bloodstream. The pituitary gland then releases TSH when it detects insufficient thyroid hormone.

TSH tells your thyroid to "release more hormone." This is why your TSH rises when your thyroid is underactive. A high TSH means that the pituitary gland is releasing its hormone to try to get the thyroid to respond and produce more thyroid hormone.

On the opposite end, when your pituitary gland senses that there is too much thyroid hormone circulating, then it slows down or even stops releasing TSH. The lowering of TSH means that your thyroid is no longer getting a message to release hormone, and thyroid hormone production will slow down.

The Controversy Over the Reference Range, or What's Normal

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While the majority of traditional doctors in the U.S. agree that the TSH test is their preferred way to diagnose and manage hypothyroidism or hyperthyroidism, they do not agree on how to interpret the TSH test results.

Until 2002, the official TSH "normal range" that laboratories and most doctors used throughout the U.S.was a range of 0.5 to 5.0.

Using that range, a TSH under 0.5 (a low TSH) indicated hyperthyroidism (an overactive thyroid), and a TSH over 5.0 (a high TSH) indicated hypothyroidism (an underactive thyroid.)

The Revised Reference Range

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Since late 2002, there has been disagreement among experts regarding the TSH reference range. For several years, the American Association of Clinical Endocrinologists (AACE) and other professional groups recommended a narrower range of .3 to 3.0. This means that hyperthyroidism was suspected at TSH levels below .3, At levels above 3.0, a diagnosis of hypothyroidism was considered.

What the American Association of Clinical Endocrinologists Said...

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Here is an excerpt from a January 2003 AACE press release:

"Until November 2002, doctors had relied on a normal TSH level ranging from 0.5 to 5.0 to diagnose and treat patients with a thyroid disorder who tested outside the boundaries of that range. Now AACE encourages doctors to consider treatment for patients who test outside the boundaries of a narrower margin based on a target TSH level of 0.3 to 3.0. AACE believes the new range will result in proper diagnosis for millions of Americans who suffer from a mild thyroid disorder, but have gone untreated until now."

Endocrinologists Change Their Minds

After the 2003 announcement, AACE and other endocrinology groups again questioned the narrowing of the ranges, and removed their recommendation that the guidelines be narrowed. The TSH Reference Range Wars continue.

Where Are We Now?

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Currently, most laboratories in the United States still use the old 0.5 to 5.0 range as their reference range for the TSH test.

This means that when the doctor gets your test report back, and they look for results flagged as abnormal, anything between .5 and 5.0 will not be flagged.

Doctors who don't know about the controversies over the reference range, and rely on flagging of results by labs as high/low/abnormal, continue to use the older guidelines. 

In other cases, doctors have deliberately chosen not to follow the recommended new guidelines. These doctors will not diagnose hyperthyroidism in people with TSH levels between 0.3 and 0.5. They also will not diagnose hypothyroidism in the many millions of Americans with a TSH level between 3.0 to 5.0.

This means that being told your TSH test is "normal" is not meaningful information. You can have a TSH of 4.0, and be told by one doctor that you are normal, and by another that you are hypothyroid and require treatment.

Your TSH can be normal, but you can still have symptoms.

The Four Questions You Need to Ask Your Doctor

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Instead of "your TSH was normal," what you really need to know from your doctor are the answers to four critical questions:

  • What was my exact TSH test result number?
  • What is the reference range at the lab where my test results were processed?
  • What reference range do you follow in diagnosing and managing thyroid disease?
  • What is your target TSH level for the best and safest resolution of my symptoms?

Be sure that you find out the specific answers to these questions before you let your doctor rule out a thyroid problem, or tell you your thyroid is "normal."

A Word from Verywell

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Understanding your TSH test results is a key foundation for all thyroid patients. To learn more about TSH testing, and the controversy over the reference range, read the following:


Braverman, L, Cooper D. Werner & Ingbar's The Thyroid, 10th Edition. WLL/Wolters Kluwer; 2012.

Garber, J, Cobin, R, Gharib, H, et. al. "Clinical Practice Guidelines for Hypothyroidism in Adults: Cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association." Endocrine Practice. Vol 18 No. 6 November/December 2012.


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