When should a high TSH lead to a higher thyroid hormone dose?
Ask the doctor
Q. I had a thyroidectomy a few years ago, and have been taking levothyroxine daily since then. My dose has been stable. While my T3 and T4 levels are still normal, my TSH is now above the normal range. Other than some fatigue, I feel okay. Do I need to increase my dose?
A. TSH stands for thyroid-stimulating hormone. It's a simple blood test. Doctors order a TSH blood test if a person has symptoms that suggest a thyroid problem, or is taking thyroid medication, such as levothyroxine, to see if the dose is correct.
Thyroid-stimulating hormone is made by the pituitary gland in the brain, then released into the bloodstream. When TSH reaches the thyroid gland, it stimulates the gland to produce more thyroid hormone.
If the blood levels of thyroid hormones (T3 and T4) drop below the normal range, the TSH level rises. If there is too much thyroid hormone in the blood, the TSH level gets very low.
An abnormally high TSH level almost always indicates an underactive thyroid gland (hypothyroidism). A very low TSH level usually means there is too much thyroid hormone in the blood (hyperthyroidism).
There are some rare causes of an underactive thyroid gland with a low TSH — for example, if a person has a diseased pituitary gland.
TSH is a more sensitive indicator of thyroid function or correct thyroid dose than T3 or T4. Similar to you, many people have a high TSH with T3 and T4 that fall into the normal range. Usually, the T3 and T4 will be at the low end of normal when the TSH is high.
Here are some reasons why your TSH might be rising:
- Most people take a generic version of levothyroxine. You might be taking levothyroxine made by a different company than the pills you took before.
- Have you started any new supplements or medications? Iron, other supplements, and certain medications can interfere with absorption of levothyroxine. Check with your pharmacist about drug interactions.
- Certain foods can lower the absorption of levothyroxine. Maybe you started taking your thyroids pills with meals. It's best to take your pills one hour before eating.
You didn't mention your actual lab values. If the TSH level is higher than the upper limit of normal and your T3 or T4 level is on the low side of the normal range, you and your doctor can discuss a possible minor increase in your thyroid dose.
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About the Author
Howard E. LeWine, MD, Chief Medical Editor, Harvard Health Publishing; Editorial Advisory Board Member, Harvard Health Publishing
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