A doctor may request for thyroid function tests if he or she believes you have a low thyroid-stimulating hormone (TSH) levels or low TSH and low T4. This is because changes in the normal TSH levels may signify a thyroid problem. Knowing if you have low TSH symptoms and/or low T4 symptoms can help the doctor figure out the best thyroid treatment plan for you.
Low TSH and Low T4 | What Does It Mean to Your Body?
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The Thyroid Feedback Loop
To understand the effects of low TSH level, you need to learn about the hypothalamic-pituitary-thyroid axis. The thyroid glands create two important hormones converted from iodine, which are thyroxine (T4) and triiodothyronine (T3). These are different hormones that work together to regulate a lot of body processes, including metabolism, moods, and heartbeat. They are also essential in controlling body temperature.
The production and secretion of the thyroid hormones, though, is more intricate than you think. In fact, it follows a feedback system, which is the axis.
For the thyroid glands to produce these hormones, it needs stimulation from the pituitary gland, which secretes TSH. This gland, though, works in conjunction with the hypothalamus in the brain. What it does is to produce the thyrotropin-releasing hormone. This hormone then compels the pituitary to create TSH. The hypothalamus, meanwhile, is sensitive to the levels of the thyroid hormones in the bloodstream.
Low TSH Symptoms and Low T4 Indications
It is normal for the serum TSH levels to change. In fact, it may vary throughout the day. This is because all the involved body parts aim to achieve balance. The problem comes in when the TSH levels are consistently abnormal. They may reveal low TSH symptoms such as low T4.
Here are the possible effects of either low T4 or low TSH levels:
1. Abnormal Thyroid Levels
TSH closely relates to the thyroid hormones changes in one can affect the other. After all, everything works in a loop or feedback system. High TSH levels, for example, may mean the thyroid is not producing sufficient hormones. If you have a low TSH level, it could mean you have a lot of circulating thyroid hormones. Chemical interaction in the body may then result in different thyroid symptoms.
2. Low TSH Test Results
One of the ways to determine problems with your TSH is through a blood test. The results of your TSH test can help determine if you have a thyroid disease. The doctor, though, may recommend taking it along with other thyroid tests.
Usually, if you have low TSH symptoms, it may mean subclinical hyperthyroidism if T4 and T3 are normal. If your TSH levels high, then you may have subclinical hypothyroidism. If the TSH level is low but T4 is high, it may be hyperthyroidism.
TSH levels may drop due to TSH suppression. It happens when the hypothalamus senses the blood has a lot of the thyroid hormones. It then “tells” the pituitary gland to release less TSH. Keep in mind there are many reasons why TSH levels can drop. One of these is pregnancy. A thyroid medication such as levothyroxine can also affect the results.
3. High TSH Levels
T4 is one of the main thyroid hormones. When your thyroid produces less of it, the hypothalamus compels the pituitary glands to release more TSH. TSH then forces the thyroid glands to produce more T4. When you are taking a blood test, you may see elevated TSH levels.
4. Slow Metabolism
The T4 hormone is biologically inactive. It needs the help of certain organs such as the liver to convert it to T3. The thyroid, though, produces about 80% more of it than T3. Both hormones also bind themselves to proteins such as thyroxine-binding globulin. By doing this, the body develops a reservoir of the hormones. The free forms are the ones that circulate and act on the cells. When there are changes to the levels of free T4 or T3, there are also effects on the metabolism. For one, it may slow down.
5. Pituitary Problems
When you have low thyroid levels, your doctor proceeds to investigate the thyroid function. The purpose is to identify the root cause. Perhaps your thyroid levels are out of whack due to thyroid nodules or toxic multinodular goiter. In worst cases, you may have thyroid cancer. In developing countries, it may indicate iodine deficiency.
In particular circumstances, the problem may not be the thyroid at all. You may have a low TSH level because of issues with the pituitary gland. One of the common causes is a tumor.
Watch this video from Dr.Cheimlich to find out more about the interpretation of thyroid test results based on the levels of your thyroid hormones:
A low TSH level can have its gray areas. That’s why doctors often recommend you don’t take a single thyroid test. In fact, they consider your other medical problems. It doesn’t undermine the fact changes in the TSH values will always need a follow-up.
Have you had a low TSH and low T4 at the same time? Share your experience with us in the comments section below!
Editor’s Note – This article has been updated for accuracy and relevancy. Original publish date: August 11, 2017.