What is a High Tsh Level?

Has your doctor told you your TSH level is high? Find out what this means – and what are other blood tests are needed if you have a high TSH level.

The thyroid gland weighs less than an ounce – but don’t underestimate its importance. This tiny, butterfly-shaped gland located in the neck controls the body’s metabolic rate – or the rate at which the body uses energy. Not surprisingly, problems with the thyroid gland can cause a host of symptoms because of its critical role in metabolism. One test that’s used to look more closely at thyroid function is the TSH test. What does a high TSH mean?

A High TSH Level Usually Means Thyroid Disease

TSH is made by a hormone-producing gland called the pituitary gland. Once produced, TSH signals the thyroid gland to release more T3 and T4. These are thyroid hormones that directly impact the body’s metabolic rate. If the thyroid gland becomes under-active from thyroid disease, it doesn’t produce enough T3 and T4. The pituitary senses the lack of thyroid hormone and starts pumping out more TSH to try to “jump start” the under-active thyroid gland. This causes TSH levels to rise, but T3 and T4 remain stubbornly low because the thyroid isn’t responding.  

What Does a High TSH Mean?

When a doctor suspects an under-active thyroid gland, he or she will draw a tube of blood to check levels of TSH, T3, and T4 – as a way to check up on thyroid function. If the lab finds a high TSH level and low T3 or T4 levels, it usually indicates hypothyroidism, or an under-active thyroid gland. In some cases, T3 or T4 can be in the normal range while TSH is elevated, which usually means a person has very mild thyroid dysfunction. In cases of early hypothyroidism, the T3 may be normal.

In rare cases, a high TSH level can come from a pituitary tumor, especially if T3 and T4 are also elevated. In these situations, brain imaging is needed to look more closely at the pituitary gland.

A TSH level should always be included when testing for thyroid disease since it’s a more sensitive measure of thyroid disease than T3 and T4. Measuring T3 and T4 levels alone can miss cases of hypothyroidism

A High TSH Level Needs Further Investigation

A high TSH level usually means the thyroid isn’t producing enough thyroid hormone, but it doesn’t say why. For this reason, other tests are needed to find the underlying cause for an under-active thyroid gland.


Merck Manual. 18th Edition. 2006.

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