Everything You Ever Wanted to Know About the TSH Thyroid Test

TSH, thyroid stimulating hormone, TSH test, thyroid test

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If you have a thyroid problem, or even suspect you have one, there is almost no way to escape the everpresent TSH test.

TSH stands for thyroid stimulating hormone. This test measures the TSH, which is produced by your pituitary gland. The pituitary is a small gland located in the brain. The TSH hormone is released as a messenger, to say to your thyroid: "produce more thyroid hormone!"

When your TSH rises, that means that the pituitary gland has detected that your thyroid hormone levels are too low, a condition known as hypothyroidism. By producing more TSH and releasing it, the pituitary is sending the message to your thyroid gland to ramp up production of more thyroid hormone.

Conversely, when your pituitary gland detects that you have more than enough thyroid hormone circulating, it cuts back on production of TSH. That reduction in TSH is also a message to your thyroid gland, saying "slow down the production of thyroid hormone." So a low TSH can be an indicator that your thyroid gland is overproducing thyroid hormone, a condition known as hyperthyroidism.

The TSH test is referred to by many endocrinologists and conventional doctors as the "gold standard" for diagnosing a thyroid condition. For many people, it may be the only test that is used to diagnose or rule out a thyroid condition or to manage your dosage of thyroid hormone replacement medication.

But do you really understand the TSH test, what it's measuring, what the numbers mean, and how it affects your health?

Resources for Understanding the TSH Test

Because so much about thyroid diagnosis and management centers around the TSH test, it is very important that anyone with a thyroid condition, as well as their advocates are caretakers, are informed and knowledgeable about this test, and what TSH test results mean.

How do you get up to speed about the TSH test? Here are some resources to help you understand this central concept in thyroid diagnosis and management. 

  1. A good starting check for understanding the TSH test is this fast recap, essentially a crash course on the TSH test. In less than a minute, you will understand the essentials.
  2. Many patients write to me to ask what to do if TSH results are normal, but they still don't feel well. This is such a common question that we have an article devoted just to this topic: What should I do if my TSH results are normal but I still have symptoms? 
  3. Here's a question about TSH test results that doctors rarely discuss with you, but comes up all the time with many patients. Why does TSH sometimes fluctuate greatly from one test to the next?
  4. One thing seems to be a sticking point for many is the relationship between TSH levels and your dosages of thyroid hormone replacement medication. The key question: Why, when TSH goes up, does the dosage of medicine also go UP?
  5. When it's time to get the actual thyroid blood tests, read our article on optimum time and conditions for TSH tests: when should you test, and should you fast before testing?
  1. What if your TSH is normal? Should you still be treated? Some doctors say yes, but only if you also have antibodies that point to Hashimoto's thyroiditis. Some cases of Hashimoto's should be treated even when the TSH is normal because it can help prevent increased antibody levels and progression to full hypothyroidism.

The TSH Reference Range Controversy

Perhaps of greatest importance to thyroid patients is awareness of the ongoing controversy over the approved reference range for TSH, sometimes referred to as the "normal range." Back in the early 2000s, endocrinologists announced that the TSH normal range was being narrowed. These new guidelines meant millions more Americans were considered hypothyroid under the new range and standards, and could conceivably be diagnosed and treated for their underactive thyroid conditions. This was a dramatic change of position for the endocrinology community.

Unfortunately, almost two decades later, the endocrinology community has since reversed its position, and gone back to the original reference ranges. This again excludes many people who have subclinical or borderline thyroid disease, who would have been diagnosed and treated under the narrow reference range.

At this point, some doctors use their own discretion and consider a narrower TSH reference range to be more accurate. Still, most endocrinologists and ​many conventional doctors continue to use the old reference range standards. 

A Word from Verywell

It can't be emphasized enough. As a thyroid patient, you need to know and understand three key concepts

  1. What the TSH test is measuring
  2. What TSH test results mean
  3. The TSH test reference range your doctor is using to diagnose and manage your thyroid condition

Finally, sure to bookmark and/or print the handy reference chart on ​key thyroid function tests and values.

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