What Is Thyroid Stimulating Hormone
Thyroid stimulating hormone is produced and released into the bloodstream by the pituitary gland. It controls production of the thyroid hormones, thyroxine and triiodothyronine, by the thyroid gland by binding to receptors located on cells in the thyroid gland. Thyroxine and triiodothyronine are essential to maintaining the bodys metabolic rate, heart and digestive functions, muscle control, brain development and maintenance of bones.
In People Without Known Thyroid Disease
A high TSH in people who are not undergoing thyroid disease treatment usually indicates the presence of primary hypothyroidism.
This is by far the most common form of hypothyroidism, and it occurs because the thyroid gland produces an inadequate amount of thyroid hormones. The pituitary gland senses these low levels and increases the production of TSH.
An elevated TSH may also occur with normal thyroid function due to the presence of antibodies, proteins made by the immune system.
Causes Of Low Tsh Levels
Autoimmune disorders are the most common cause of hyperthyroidism. Of these disorders, Grave’s disease is the most well-known. Other conditions that can cause hyperthyroidism include:
- Toxic nodules on your thyroid
- Thyroid gland dysfunction due to a medication
- Excess thyroid hormone therapy
- Other autoimmune disorders
A goiter is an enlarged thyroid. Thyroids can grow nodules on them, and if more than one grows, it is called a multinodular goiter, which produces too much thyroid hormone. These nodules can also be toxic and cause the thyroid not to function as it should.
Certain medications can also affect the production of TSH in your pituitary gland, which can cause the thyroid not to produce the correct level of hormones. Corticosteroids, dopamine, and some somatostatin drugs can inhibit the pituitary’s production of TSH .
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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.
What Is Low Tsh
The endocrine system is responsible for regulating the function of organs in your body. The pituitary gland produces thyroid stimulating hormone . TSH stimulates the thyroid gland to produce thyroid hormones.
If the pituitary gland is not functioning to produce TSH as it should, then the thyroid will not make the level of hormones it should be. This reduction of hormones from the thyroid can lead to many health problems.
Low TSH levels can affect your health, quality of life, and your relationships. The signs of the conditions caused by a low TSH level are essential to know so that you can recognize that you might have a health issue and discuss it with your doctor to get the proper treatment.
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What Is A T3 Test
T3 TestsT3 tests measure triiodothyronine levels in the blood. A Total T3 test measures the bound and free fractions of triiodothyronine. Hyperthyroid patients typically have an elevated Total T3 level. T3 tests can be used to support a diagnosis of hyperthyroidism and can determine the severity hyperthyroidism.
In some thyroid diseases, the proportions of T3 and T4 in the blood change and can provide diagnostic information. A pattern of increased T3 vs T4 is characteristic of Graves disease. On the other hand, medications like steroids and amiodarone, and severe illness can decrease the amount of thyroid hormone the body converts from T4 to T3 resulting in a lower proportion of T3.
T3 levels fall late in the course of hypothyroidism and therefore are not routinely used to evaluate patients with underactive or surgically absent thyroid glands.
Measurement of Free T3 is possible, but is often not reliable and therefore may not be helpful.
What Does High Tsh Mean
High TSH levels can mean your thyroid is not making enough thyroid hormones, a condition called hypothyroidism. Low TSH levels can mean your thyroid is making too much of the hormones, a condition called hyperthyroidism.
What are the side effects of high TSH levels?
- swelling of the face and neck.
- increased sensitivity to cold temperatures.
- dry skin.
- a slow heart rate.
- irregular or heavy menstrual periods.
What is the cause of high TSH levels? Your TSH levels will be increased, if: Your thyroid gland is not working as it normally should. Your thyroid gland is infected or inflamed, as in Hashimotos thyroiditis, or autoimmune thyroiditis. This occurs when your body is attacking your thyroid gland, for some unknown reason.
What is considered a dangerously high TSH level?
Experts dont 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.
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Your complete thyroid blood panel should include TSH, free triiodothyronine , free thyroxine ,and TPO antibodies. Having this information helps to determine the cause of your under- or over-active thyroid.
Lab results read as positive or negative concerning whether you have TPO antibodies present in your blood sample.
Suppose you show a negative result for TPO antibodies. In that case, it means that there were no TPO antibodies discovered in your blood. Therefore, if you have symptoms of a thyroid condition, it is unlikely that an autoimmune disorder causes them.
If you show a positive result for TPO antibodies, it may mean you have:
The diagnosis is made if you have high levels of TPO antibodies and high levels of thyroglobulin a protein produced by the thyroid.
The diagnosis is made if you have high levels of TPO antibodies and high levels of thyroid-stimulating hormone receptor antibodies.
A TPOAb test is not the only indicator of Hashimotos. A study from California Northstate University suggests that 10% of patients with Hashimotos may have negative blood work for TPO antibodies.
Use the same laboratory
Test results are only meaningful when compared to reference ranges. Reference ranges are the values expected for a healthy person.
What Tsh Level Requires Treatment
The American Thyroid Association recommends that patients older than 65, should be treated for hyperthyroidism if TSH levels are below 0.1 mIU/L. Patients younger than 65 are treated if they are post-menopausal women, have coexisting conditions such as heart disease or osteoporosis, or symptoms of hyperthyroidism.
Subclinical hyperthyroidism with TSH levels between 0.1 to 0.4 mIU/L with normal T3 and T4 levels may be just monitored if the patient is below 65 and has no symptoms. Patients above 65 or those below 65 with comorbidities or symptoms of hyperthyroidism may be treated depending on their condition.
Doctors usually start treatment for hypothyroidism if the TSH level remains persistently elevated above 10.0 mIU/L even if T4 is normal and the patient has no symptoms. Thyroid levels are usually periodically monitored and maintained optimally with appropriate dosage changes.
Subclinical hypothyroidism, which means TSH levels of 5.0 to 10.0 mIU/L and normal T4, may require treatment if the individual has a positive thyroid antibodies test, experiences symptoms, or is at high risk for developing hypothyroidism.
If you have questions about TSH levels, ask your doctor to explain what your TSH level means.
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What Is The Reason For High Tsh Levels
High levels typically indicates an underactive thyroid gland, which produces too little thyroid hormone. This is known medically as hypothyroidism.
Common causes of hypothyroidism include an autoimmune disease , radiation treatment, or surgical removal of the thyroid gland.
Replacing thyroid hormone and altering your diet are crucial for the safe and effective treatment of an underactive thyroid.
Summary: High TSH levels for the average adult are 4.2 mIU/L and over. This reading typically indicates an underactive thyroid.
High Levels Of Tsh Hypothyroidism
If a person has TSH levels more than normal, it means that he has an underactive thyroid gland. This condition is known as hypothyroidism in which the thyroid gland does not produce enough hormones. In this condition, the thyroid gland enlarges leading to goitre. The person may feel lethargic, cold and puts on weight. Patients suffering from this condition, show symptoms that are linked to slow metabolic rate. The condition may not be prominent in the initial stages, but over time, if left untreated, it can lead to several related health issues such as joints pain, infertility, obesity and even heart diseases.
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How Much Does The Test Cost
The cost of a TSH test will vary depending upon factors such as where it is performed and whether or not you have insurance coverage. Insurance will usually cover the cost of TSH testing if your doctor orders it to diagnose or treat a medical condition. You can check with your doctor, the lab, or your insurance company to learn more about the cost and what, if any, out-of-pocket costs you may be responsible for.
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Iodine Deficiency Or Excess
Both iodine deficiency or excessive iodine intake can result in an elevated TSH .
Globally, the most common cause of hypothyroidism is iodine deficiency .
Thyroid hormones are made from the chemical iodine, which humans need to get from the food they eat. Not getting enough iodine in the diet can lead to hypothyroidism, and may even cause goiters .
Many studies also show that excessive iodine intake can also lead to hypothyroidism .
For example, children living in an area with abnormally high iodine concentrations in their drinking water show higher rates of thyroid dysfunction .
Animal and cell studies show that excess iodine can be toxic to the thyroid gland and lead to thyroid cell death .
Patterns Of Thyroid Tests Associated With Thyroid Disease
Primary Hypothyroidism A high TSH and low thyroid hormone level can indicate primary hypothyroidism. Primary hypothyroidism occurs when the thyroid gland makes too little thyroid hormone. Symptoms of hypothyroidism can include feeling cold, constipation, weight gain, slowed thinking, and decreased energy. Causes of primary hypothyroidism include:
- Autoimmune thyroid disease, including Hashimoto’s thyroiditis
- Thyroid gland dysfunction due to a medication
- Removal of all or part of the thyroid gland
- Radiation injury to the thyroid
- Excess treatment with anti-thyroid medications
Early or mild hypothyroidism may present as a persistently elevated TSH and a normal FT4 hormone level. This pattern is called subclinical hypothyroidism and your doctor may recommend treatment. Over time, untreated subclinical hypothyroidism can contribute to heart disease.
It is important to remember that normal TSH levels in older individuals are higher than the normal ranges for younger individuals.
Primary Hyperthyroidism A low TSH and a high thyroid hormone level can indicate primary hyperthyroidism. Primary hyperthyroidism occurs when the thyroid gland makes or releases too much thyroid hormone. Symptoms of hyperthyroidism can include tremors, palpitations, restlessness, feeling too warm, frequent bowel movements, disrupted sleep, and unintentional weight loss. Causes of primary hyperthyroidism include:
Why Would I Need These Tests
The thyroid gland‘s hormones help control some of your body’s metabolic processes, such as heart rate, blood pressure, body temperature and weight. Too much or too little of these hormones can make you ill.
You might need thyroid tests if:
- you have symptoms of hyperthyroidism or hypothyroidism
- you are taking some form of thyroid hormone replacement treatment
- you are female and being investigated for infertility
Very rarely, babies are born without a working thyroid gland. For this reason, all Australian newborns are screened for hypothyroidism with a TSH test using a drop of blood taken from a heel prick.
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How Does The Thyroid Gland Function
The major thyroid hormone secreted by the thyroid gland is thyroxine, also called T4 because it contains four iodine atoms. To exert its effects, T4 is converted to triiodothyronine by the removal of an iodine atom. This occurs mainly in the liver and in certain tissues where T3 acts, such as in the brain. The amount of T4 produced by the thyroid gland is controlled by another hormone, which is made in the pituitary gland located at the base of the brain, called thyroid stimulating hormone . The amount of TSH that the pituitary sends into the bloodstream depends on the amount of T4 that the pituitary sees. If the pituitary sees very little T4, then it produces more TSH to tell the thyroid gland to produce more T4. Once the T4 in the bloodstream goes above a certain level, the pituitarys production of TSH is shut off. In fact, the thyroid and pituitary act in many ways like a heater and a thermostat. When the heater is off and it becomes cold, the thermostat reads the temperature and turns on the heater. When the heat rises to an appropriate level, the thermostat senses this and turns off the heater. Thus, the thyroid and the pituitary, like a heater and thermostat, turn on and off. This is illustrated in the figure below.
Questions To Ask Your Endocrinologist:
- What tests do I need to check my thyroid levels?
- What are the normal ranges for each hormone?
- Are my T3, T4, and TSH levels normal?
- Are my symptoms indicative of a thyroid disorder?
- How can we correct any issues with the levels through medication or lifestyle changes?
- Are there any side effects to the medications?
- How long does it take before the medicine starts to work?
How Is Hypothyroidism Diagnosed
It can actually be difficult to diagnose hypothyroidism because the symptoms can be easily confused with other conditions. If you have any of the symptoms of hypothyroidism, talk to your healthcare provider. The main way to diagnose hypothyroidism is a blood test called the thyroid stimulating hormone test. Your healthcare provider may also order blood tests for conditions like Hashimotos disease. If the thyroid is enlarged, your provider may be able to feel it during a physical exam during an appointment.
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Are There Any Other Tests For The Diagnosis Of Hyperthyroidism
The vast majority of cases of hyperthyroidism are diagnosed by the combination of clinical history, initial laboratory screening tests, and the determination of T4 or fT4 blood concentrations.
On rare occasions, additional tests such as the T3 suppression test or advanced imaging studies of the thyroid gland may need to be performed. Imaging studies are usually done at a referral center.
Is There Anything Else I Need To Know About A Tsh Test
Thyroid changes can happen during pregnancy. These changes are usually not significant, but some women can develop thyroid disease during pregnancy. Hyperthyroidism occurs in about one in every 500 pregnancies, while hypothyroidism occurs in approximately one in every 250 pregnancies. Hyperthyroidism, and less often, hypothyroidism, may remain after pregnancy. If you develop a thyroid condition during pregnancy, your health care provider will monitor your condition after your baby is born. If you have a history of thyroid disease, be sure to talk with your health care provider if you are pregnant or are thinking of becoming pregnant.
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Too Much Synthetic T4 Hormones
Thyrotoxicosis factitia is a condition caused by taking too much synthetic T4 hormones . It mimics an extremely overactive thyroid. Thyroglobulin levels are very low or undetectable in people with this condition .
Thyroglobulin can help doctors determine if an overactive thyroid is due to TF or other causes .
Make sure to use levothyroxine only if your doctor prescribed it, and strictly follow their dosage instructions.