Thyroxine Triiodothyronine And Tsh Levels
The main job of the thyroid gland is to make the hormone thyroxine, also known as T4 because it has four iodine molecules. The thyroid also makes the hormone triiodothyronine, known as T3 because it has three iodine molecules, but in smaller amounts, explains Cathy Doria-Medina, MD, an endocrinologist with HealthCare Partners Medical Group in Torrance, California. The thyroid gland makes mostly T4, the T4 has to be converted to T3, because T3 is the part of thyroxine that actually does the work, she says.
The pituitary gland at the base of the brain controls hormone production in your body. It makes thyroid-stimulating hormone , which tells the thyroid gland how much T4 and T3 to produce. The TSH level in your blood reveals how much T4 your pituitary gland is asking your thyroid gland to make. If your TSH levels are abnormally high, it could mean you have an underactive thyroid, or hypothyroidism. Thats because it indicates your pituitary gland is producing more TSH in an effort to stimulate your thyroid to produce thyroid hormone, according to the Mayo Clinic.
TSH levels go in the opposite direction of your thyroid hormone, Dr. Doria-Medina explains. If youre making too little thyroid hormone, your TSH will go up. If youre making too much thyroid hormone, your TSH will go down.
If your TSH is higher than 4.0 mU/L on repeat tests, you probably have hypothyroidism.
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 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.
Cysts Or Nodules In The Thyroid Gland
Nodules or cysts in the thyroid gland can affect its function and cause too little T4 and T3 to be produced. This has the effect of increased secretion of TSH which can cause levels to increase above 4.0 mIU/L.
The journal Medical Clinics of North America reports that testing for high levels of TSH is essential in monitoring thyroid nodules. Blood serum tests for TSH are usually combined with ultrasound scans to check for cancerous cells in the thyroid. Doctors say that constant monitoring is essential because low T4 in the blood along with normal or high TSH can increase the risk that nodules become malignant.16
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Questions To Ask Your Doctor
Its important to ask questions so that you are well-equipped to engage with your doctor in a discussionpossibly an ongoing oneabout the best thyroid management plan for you. Good questions to pose to your doctor include:
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What is the cause of my underactive thyroid ?
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Do I have Hashimotos disease ?
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What do the results of my blood test mean?
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How long will I need medicine for my hypothyroidism and what are the side effects?
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What TSH level will you use as a target for me?
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After I’m in the optimal range, how often do you suggest I come back for blood tests to make sure my dosage needs havent changed?
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Am I at risk for related health problems?
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How quickly can I expect relief from my hypothyroid symptoms?
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Are there any lifestyle changes I can make to relieve my symptoms?
How Is Subclinical Hypothyroidism Diagnosed
Thyroid values like TSH are measured in blood tests. Because a single test can be misleading, a second test is usually done 2 or 3 months later. In both tests, the blood is taken at the same time of day because TSH levels can fluctuate over the course of 24 hours. Subclinical hypothyroidism is diagnosed when both TSH readings are high but the thyroid hormone thyroxine is still within the normal range.
Experts don’t agree on which TSH levels should be considered too high. Some suggest that TSH levels of over 2.5 milliunits per liter are abnormal, while others consider levels of TSH to be too high only after they have reached 4 to 5 mU/L.
Both children and teenagers as well as older people have somewhat higher TSH levels than middle-aged people. Because of this, thyroid specialists have been debating whether a higher threshold should be used for these age groups. Being severely overweight and certain medications can also increase TSH. TSH levels are likely to fluctuate more during pregnancy.
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High Tsh In Pregnancy
It is normal during pregnancy for T4 levels to increase which causes TSH levels to drop. According to Dr. Sandra Fryhofer on Medscape, T3 and T4 thyroid hormones can increase by up to 50% during pregnancy. Even though some labs put the normal TSH range for pregnancy as high as 5 mIU/L, Dr. Fryhofer recommends a much lower level.
The recommendations for TSH during pregnancy are as follows:
- First trimester: 0.1 2.5 mIU/L
- Second trimester: 0.2 3.0 mIU/L
- Third trimester: 0.3 3.0 mIU/L
If TSH levels are higher than 2.5 mIU/L during pregnancy, Dr. Fryhofer recommends testing for levels of T4 to check for hypothyroidism in pregnancy.
Thyroid Removal Or Thyroid Deactivation
If you have had surgery to remove your thyroid or radioiodine therapy to deactivate your thyroid, you will receive regular T4 replacement therapy. This usually affects TSH levels secreted by your pituitary gland as your medication is monitored and adjusted.
The journal Rambam Maimonides says that low levels of T3 and T4 exert a negative feedback on TSH and signals to your body to increase TSH levels. When receiving levothyroxine therapy, your TSH levels and T4 levels will be closely monitored to make sure that T4 levels dont drop dangerously low.14
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Mild Hypothyroidism: Who Should Be Treated
What to do about mild hypothyroidism is a subject that has been studied and debated for years. Mild hypothyroidism is also called subclinical hypothyroidism. It doesn’t meet the standard definition of overt hypothyroidism. You may have no symptoms, and your thyroid function blood tests show a mixed picture.
Your free T4 level is normal, meaning your body is getting enough thyroid hormone. It is your TSH level that is above the normal range, which indicates your thyroid gland has to work harder to pump out that thyroid hormone.
One worry about mild hypothyroidism is the potential link between untreated subclinical hypothyroidism and coronary artery disease. Results of research on whether subclinical thyroid disease causes heart problems have been conflicting. However, the condition has been associated with heart and blood vessel abnormalities, and some studies suggest that treating mild hypothyroidism can improve various markers of heart structure and function.
However, there are potential downsides to treating subclinical hypothyroidism. There is the risk of overtreatment, which might cause symptoms, such as feeling jittery and insomnia. Also, long-term overtreatment can lead to loss of bone density.
If your TSH level is higher than 10 mIU/L, you should start treatment, because you will very likely develop symptoms of an underactive thyroid, even if you don’t have them now.
What Does A High Tsh Mean
What can happen if the TSH level is too high? If a TSH level is too high, it may be a sign of hypothyroidism. Here are some of the symptoms of hypothyroidism:
- Enlarged thyroid
There are two main forms of hypothyroidism, or an underactive thyroid:
Another form of secondary hypothyroidism, which some even call tertiary hypothyroidism, occurs when your hypothalamus releases too little thyrotropin. This issue with the hypothalamus can affect the pituitary gland, which in turn affects the thyroid gland.
What may be causing high TSH? Autoimmune diseases such as Hashimotos, toxin exposure, or even food allergies may be causing high TSH levels, which is due to low thyroid hormone levels and hypothyroidism.
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How Does My Thyroid Work
The thyroid gland is a small, butterfly-shaped organ located in the front of your neck just under the voice box . Picture the middle of the butterflys body centered on your neck, with the wings hugging around your windpipe . The main job of the thyroid is to control your metabolism. Metabolism is the process that your body uses to transform food to energy your body uses to function. The thyroid creates the hormones T4 and T3 to control your metabolism. These hormones work throughout the body to tell the bodys cells how much energy to use. They control your body temperature and heart rate.
When your thyroid works correctly, its constantly making hormones, releasing them and then making new hormones to replace whats been used. This keeps your metabolism functioning and all of your bodys systems in check. The amount of thyroid hormones in the bloodstream is controlled by the pituitary gland, which is located in the center of the skull below the brain. When the pituitary gland senses either a lack of thyroid hormone or too much, it adjusts its own hormone and sends it to the thyroid to balance out the amounts.
If the amount of thyroid hormones is too high or too low , the entire body is impacted.
When Abnormal Thyroid Function Tests Are Not Due To Thyroid Disease
While blood tests to measure thyroid hormones and thyroid stimulating hormone are widely available, it is important to remember that no all tests are useful in all circumstances and many factors including medications, supplements, and non-thyroid medical conditions can affect thyroid test results. An endocrinologist can help you make sense of thyroid test results when there is a discrepancy between your results and how you feel. A good first step is often to repeat the test and ensure there are no medications that might interfere with the test results. Below are some common reasons for mismatch between thyroid tests and thyroid disease.
Non-thyroidal illness Significant illness, such as an infection, cancer, heart failure, or kidney disease, or recent recovery from an illness can cause changes transient changes in the TSH. Fasting or starvation can also cause a low TSH. An endocrinologist can help to interpret changes in thyroid function tests in these circumstances to distinguish non-thyroid illness from true thyroid dysfunction.
Test interference Biotin, a common supplement for hair and nail growth, interferes with many thyroid function tests and can lead to inaccurate results. Endocrinologists recommend stopping biotin supplements for 3 days before having a blood test for thyroid function.
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What Should Your Tsh Level Be
Most laboratories classify normal TSH levels as between 0.4 and 4.5 milliunits per liter , according to theAmerican Thyroid Association . A normal TSH level in most cases, usually indicates that you dont have a thyroid problem.
TheATA reports that nearly 20 million Americans have some form of thyroid disease. Yet more than 60% of those with a thyroid disorder are unaware of their medical condition.
How T3 And T4 Affect Tsh Levels
The amount of T3 and T4 in blood serum directly affects levels of TSH that the pituitary gland produces.
The journal Endocrinology says that there is a negative feedback loop that signals to the pituitary gland to produce more or less TSH. If there are low T4 and T3 in the blood, more thyroid-stimulating hormone is produced to boost T4 levels. This is why an underactive thyroid gland is associated with TSH levels above the normal reference range.5
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What Is The Thyroid
The thyroid is one of the most important glands in our body. It is situated low on the front of the neck and produces 2 thyroid hormones : thyroxine and triiodothyronine . Both of these hormones are essential for maintaining good metabolism, brain development, heart and digestive health, as well as good muscle and bone health1.
In addition, the thyroid gland produces calcitonin, a protein-based hormone that protects the body from elevated blood calcium levels, a condition known as hypercalcemia2.
In People Being Treated For Thyroid Disease
A high TSH may be found in people being treated for either hypo- or hyperthyroidism.
With hypothyroidism, a high TSH usually means that the dose of thyroid hormone replacement needs to be increased.
In some cases, however, the dose is okay, but the medication is not being fully absorbed. For example, many foods and medications can affect the absorption of Synthroid in your system. Learning what to avoid while taking this medication is important for it to work properly.
With hyperthyroidism, a high TSH usually means that the treatmentbe it surgery, radioactive iodine, or medicationswas so effective in limiting the production of thyroid hormone that it caused the person to become hypothyroid.
A low TSH often means that a person has an elevated level of thyroid hormones.
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Interpretation Of Tsh Levels
Generally, normal TSH levels are between 0.5 and 5.0 mIU/L. However, this may vary for pregnant women as TSH levels naturally change as the pregnancy progressessays James.
TSH levels below 0.5 mIU/L or above 5.0 mIU/L can indicate different types of thyroid disorders that often require additional testing to diagnose. Here is an overview of what abnormal TSH levels can mean.
How To Keep Hypothyroidism Under Control
Because youll need to take thyroid medication every day for the rest of your life, even after the right dose is found, your hormone levels will be monitored regularly to be sure that your treatment is working properly. Eventually, most people with hypothyroidism can just be seen yearly by their doctor, Doria-Medina says.
The American Thyroid Association recommends that you keep your TSH within a narrow range of 0.5 to 2.5 mU/L, but dont be alarmed if your test results vary a little. Some variation is normal because your pituitary gland sends out TSH in pulses, not a steady stream. Also, factors like the time of day youre tested can make a difference. TSH levels are likely to be higher at night and lower during the day. Some people, including those who are pregnant or those with a history of thyroid cancer, have different TSH goals. Talk to your doctor about the target TSH range thats right for you.
If you have new or worsening symptoms or your health status changes such as if you become pregnant, go through menopause, or are given another medicine that can interfere with the absorption of your thyroid hormones, such as anticonvulsants, certain antacids, or iron or calcium supplements you should see your doctor and have your blood tested again, even if its ahead of schedule.
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Can You Still Have A Problem If Your Tsh Is Normal
The TSH test is a highly sensitive indicator of your overall thyroid health, says Brittany Henderson, MD, a board-certified endocrinologist at Charleston Thyroid Center in Mount Pleasant, South Carolina. Interpretation can be difficult because there is a wide range of normal on the TSH scale.
Medications and supplements youre currently taking can affect the results of your TSH test. One example is biotin, which can falsely show low TSH levels.
Whats considered normal is influenced by several factors:
Research has shown that levels of TSH tend to increase with age, decrease with pregnancy, and vary by ethnicity.
Diagnosing Low Tsh Levels
The most common and effective test for low TSH is a blood test. In addition to analyzing your TSH level, your doctor is looking for T4 and T3 , which the thyroid produces. These three hormones give doctors an indication of which gland they should focus on, the thyroid or the pituitary.
Your doctor may send you to get some imaging testing done to get a look at your glands. An ultrasound can be performed, or a thyroid scan with slightly radioactive iodine and a special camera can look for inflammation or thyroid shrinkage.
Your thyroid may not be taking in enough iodine to produce the hormones it is supposed to to test this, doctors use the radioactive iodine uptake test, which involves a dose of slightly radioactive iodine and a special probe to check for uptake levels.
An antibody test can also be used to check for an autoimmune disorder, such as Graves disease, causing hyperthyroidism.
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