What is TSH?
The thyroid plays an essential function in the body — it releases a hormone that regulates many organs and their functions. The thyroid receives a hormone called thyroid-stimulating hormone (TSH) from the pituitary gland, which governs how the thyroid releases its hormones for organ regulation.
If the pituitary gland is not releasing the correct amount of TSH, the thyroid also doesn't release the hormone levels it is supposed to.
High TSH levels can affect your quality of life, relationships, and health. It is essential to know the signs of this condition to recognize a health issue and describe it to your doctor to get treatment.
Symptoms of high TSH levels
High levels of TSH is an indicator that your thyroid is not producing enough hormones, like thyroxine (T4) and or triiodothyronine (T3). This hormonal imbalance is called primary hypothyroidism. Sometimes high TSH causes a decrease in thyroid hormones, but they are still in normal range. This is called subclinical hypothyroidism.
Symptoms of high TSH that result in primary hypothyroidism may include
- Slow heart rate
- Puffiness in the face
- Cold intolerance
- Weight and appetite changes
- Hair loss and thinning
- Dry skin and hair
- Irregular or heavy menstruation
- Joint or muscle pain
These symptoms aren't always present at the onset of the condition. Since many of these symptoms can be caused by other conditions, you may end up having elevated TSH levels for years before you notice any symptoms.
Causes of high TSH levels
Thyroid hormones operate on a negative feedback loop. Low thyroxine levels indicate to the pituitary gland to produce more TSH, but more TSH can further decrease thyroxine (and other thyroid hormones) levels. Therefore, any issues that cause hypothyroidism, will in turn affect production from the pituitary gland.
One of the most common causes of hypothyroidism with a high TSH level is chronic autoimmune thyroiditis, also known as Hashimoto's thyroiditis. White blood cells begin to attack the thyroid gland, which decreases the amount of thyroid hormone it produces.
Other things that affect T4 levels, ultimately affecting TSH levels, include:
- Hormonal changes from hormonal birth control or a shift in estrogen levels
- Medications that cause thyroid dysfunction, like amiodarone or tyrosine kinase inhibitors
- Injury to the thyroid gland from radiation therapy
- Partial or complete removal of the thyroid gland
While the causes of thyroid diseases are widely researched and understood, it is less clear what can cause the elevated TSH levels if the pituitary gland is the source of the issue. One possible cause of elevated TSH levels are TSH-secreting adenomas. These are tumors on the pituitary that independently produce TSH, stimulating the thyroid gland to produce T4 and T3. However, these tumors are rare.
Swelling of the pituitary gland can also cause malfunction and hormonal imbalance, potentially affecting TSH levels. However, the condition is rare and usually affects other hormones produced by the pituitary.
When to see the doctor for high TSH levels
You may not know that your TSH levels are high without being tested by your doctor, so if you're experiencing any of the symptoms of hypothyroidism, see them immediately. Untreated hypothyroidism can lead to other health problems, coma, or even death.
Diagnosing high TSH levels
When you see your doctor, the most common test for a high TSH level is a blood test. They will not only check your TSH level, but they also are looking at your triiodothyronine (T3) and thyroxine (T4) levels.
Imaging tests such as an ultrasound or a thyroid scan with a special camera and slightly radioactive iodine are used to look at your thyroid. It looks for inflammation or shrinkage, which can both occur with hypothyroidism. Another test, called a radioactive iodine uptake test, is done to see if your thyroid is taking up enough iodine to make the hormones it produces.
Treatments for high TSH levels
If your TSH level is high, the treatment is usually to prescribe pure synthetic T4 (levothyroxine sodium, called LT4), which is a manufactured version of the T4 hormone your thyroid produces. If your T3 level is low, the doctor can give you Liothyronine, which is only a short-term treatment for low T3 levels.
Balancing your thyroid hormone levels, including T4 and T3, should restore the feedback loop to the pituitary gland, prompting it to produce less TSH.
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American Thyroid Association: "Hashimoto's Thyroiditis (Lymphocytic Thyroiditis)."
California Centers for Pituitary Disorders: "Hypothyroidism."
California Center for Pituitary Disorders: "Secondary hypophysitis."
California Center for Pituitary Disorders: "TSH-secreting Adenomas."
Harvard Health Publishing: "Treating hypothyroidism."
Michigan Medicine: "Radioactive Iodine Uptake Test."
National Institute of Diabetes and Digestive and Kidney Diseases: "Hypothyroidism (Underactive Thyroid)."
National Institute of Diabetes and Digestive and Kidney Diseases: "Thyroid Tests."
Physiological Reviews: "Thyroid-Stimulating Hormone and Thyroid-Stimulating Hormone Receptor Structure-Function Relationships."
UCLA Health: "What are Normal Thyroid Hormone Levels?"