Understanding the TSH Test and Its Controversies

Front view of test tubes containing blood samples
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The thyroid stimulating hormone (TSH)  blood test is considered by some physicians to be the primary—and in some cases the only—test needed to diagnose and manage an underactive or overactive thyroid, known as hypothyroidism or hyperthyroidism. The TSH test is sometimes referred to by conventional endocrinologists as the "gold standard" test for diagnosing and treating thyroid conditions.

What Does the TSH Test Measure?

The test measures the levels of TSH, a hormone that is made and released by your pituitary gland.

Your pituitary senses whether you have enough thyroid hormone in your bloodstream, and when it detects insufficient levels, your pituitary releases TSH to spur your thyroid to release more thyroid 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 your thyroid to respond by producing 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 TSH Reference Range

As of 2017, at most laboratories in the U.S. the official reference range for the TSH test runs from approximately 0.5 to 4.5 or 5.0 (mIU/L). A patient whose TSH level is within the reference range is referred to as "euthyroid," and is considered to have normal thyroid function.

The reference range—also sometimes called the "normal range"—is an important part of your overall thyroid diagnosis and treatment program, because the conventional endocrinology world considers it to be key to diagnosis and management of thyroid function.

How Is the TSH Reference Range Determined?

A TSH reference range is obtained by taking a group of people in the population, measuring their TSH levels, and calculating a range that is supposed to represent the range of TSH levels in a healthy population.

Using the typical reference range, a TSH under 0.5 (a low TSH) may be indicative of hyperthyroidism (an overactive thyroid), and a TSH over 4.5/5.0 (a high TSH) may indicate hypothyroidism (an underactive thyroid.)

The TSH Reference Range Controversy

One of the most controversial issues has been the issue of the changing "normal" reference range for the TSH test. In late 2002, the National Academy of Clinical Biochemistry (NACB) issued new guidelines for the diagnosis and monitoring of thyroid disease.

In the guidelines, the NACB reported that the TSH reference range was too wide and actually included people with thyroid disease. When more sensitive screening was done, which excluded people with thyroid disease, 95 percent of the population tested had a TSH level between 0.4 and 2.5. As a result, the NACB recommended reducing the reference range to those levels.

The NACB guidelines led to a recommendation in January 2003 by the American Association of Clinical Endocrinologists (AACE), calling for 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." The statement also said: "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."

In research published in the Journal of the American Medical Association in 2003, Dr. Vahab Fatourechi and fellow researchers estimated that if the range were narrowed according to the AACE recommendations, the total number of people with thyroid disease would expand from approximately 5 percent of the population to an estimated 20 percent of the population, with most of the added patient population falling in the hypothyroid/underactive category.

This represented a dramatic increase in the number of thyroid patients nationwide, from an estimated 15 million, to a total of some 60 million Americans.

At the same time, however, a consensus conference made up of representatives from the key professional groups involved in thyroid treatment—including the American Association of Clinical Endocrinologists, the American Thyroid Association, and the Endocrine Society—published their findings in 2004, recommending against routine treatment of patients with TSH levels of 4.5 to 10.0 mIU/L. The new reference range initiative was dropped.

Almost two decades later, America's testing laboratories still use the old reference range of and doctors remain divided. Among conventional physicians, most continue to refuse to diagnose hypothyroidism unless the TSH test results are outside the traditional reference range and flagged as abnormal by the laboratory.

Jeffrey Garber, MD, FACE, addressed the controversy on behalf of the American Association of Clinical Endocrinologists (AACE). According to Dr. Garber, guidelines are not meant to function as a replacement for the judgment of a physician's individual practice. While in his published writings, Dr. Garber has said he doesn't feel that treating subclinical hypothyroidism is typically warranted, he said that in practice, he doesn't hesitate to treat a patient with a TSH within the reference range if he judges it to be potentially helpful.

Said Garber:

The TSH normal range should not be a polarizing issue. But as often seen in medicine, it's easier to agree on the extremes. When you get closer to what's marginal, it's a harder call. We need to realize that it's a continuum. If people know that this particular group is more likely to have thyroid disease than the group that's lower, it doesn't commit you to treatment and doesn't say that it's not appropriate, it says to follow it, and maybe intervene.

The Challenge for Patients: “Your TSH Is Normal”

The TSH reference range issue poses challenges for you as a patient.

When your doctor gets your test report back, anything within the reference range will not be flagged as abnormal. That means, if your doctor relies on flagged levels and only acts on levels outside the reference range, you will not be diagnosed or have your treatment adjusted.

Ultimately, being told your TSH test is "normal" is not useful information. 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," especially if you're experiencing symptoms.

A Word From Verywell

When faced with endocrinologists or other physicians who are reluctant to diagnose by any other means than a rigid interpretation of the TSH results, it may be time to get a second opinion from an endocrinologist, or broaden your search to include a holistic MD, osteopathic physician, or a trained and licensed naturopath.

Thorough practitioners typically bring in a number of factors beyond the TSH test in the diagnosis and management of thyroid disease, including:

  • Additional blood tests, such as Free T4, Free T3, and antibody profiles
  • Clinical evaluation of visible signs of thyroid disease, including changes in reflexes, swelling and edema of the face and extremities, hair loss in head and body, loss of outer edges of eyebrows, thyroid enlargement, eye changes, heart rate, blood pressure, and other measurable signs
  • Imaging tests to identify thyroid enlargement, atrophy, and nodules
  • A personal and family medical history
  • A treatment goal of  "optimal" TSH levels and resolution of symptoms

Sources:

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

Fatourechi V, Klee GG, Grebe SK, et al. Effects of reducing the upper limit of normal TSH values. JAMA. 2003;290:3195-3196.

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.​

Gursoy A, et. al. "Which thyroid-stimulating hormone level should be sought in hypothyroid patients under L-thyroxine replacement therapy?" Int J Clin Pract. 2006 Jun;60(6):655-9

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