TSH (Thyroid-Stimulating Hormone)
Why have this test?
This Thyroid-Stimulating Hormone is used to check for and diagnose disorders of the thyroid. It is also used to monitor the ongoing treatment of both hyperthyroidism and hypothyroidism.
When Should You be Tested?
Screening is commonly recommended for newborns. There is no medical consensus as to the adult age for screening or whether adult screening should be standard.
Treatment monitoring: As recommended by your medical provider
Other Situations: If an individual has an enlarged thyroid and/or has experienced the symptoms of hypothyroidism or hyperthyroidism.
Required Sample Type: A sample of blood taken from a vein in the arm, or for infants, from pricking the heel.
Preparation for the Test: There is no specific preparation necessary. Some medications can interfere with the TSH testing. Let your medical providers know about any medications that you take. If you regularly take thyroid hormones to treat a disease of the thyroid, you should have your blood sample drawn before taking your hormone dose for the day.
What Does This Test Measure?
Thyroid-stimulating hormone (TSH) is produced by the pituitary gland. This is a very small organ behind the sinus cavities and below the brain. TSH triggers the thyroid gland to release the thyroid hormones thyroxine (T4) and triiodothyronine (T3) into the bloodstream. These hormones regulate the rate at which the body consumes energy. This laboratory test measures the amount of TSH in the blood at a given time.
Thyroid-stimulating hormone, combined with TRH, which is released by the hypothalamus, make up the system that the body uses to keep consistent amounts of thyroid hormones in the bloodstream at all times. If these hormone concentrations drop, the pituitary gland increases the production of TSH.
Thyroid-stimulating hormone then stimulates production and release of significantly more T3 and T4 by the thyroid, which is a small gland at the base of the throat shaped like a butterfly. If all these organs are working correctly, the thyroid production turns itself on and off appropriately to keep the correct hormone levels in the bloodstream.
However, if the thyroid releases too much T3 and T4, the individual can suffer from the symptoms of hyperthyroidism like rapid heartbeat, weight loss, nervousness, trouble sleeping, and hand tremors. The most common cause of hyperthyroidism is Graves’ disease, which is a chronic autoimmune disease. Patients with this diagnosis deal with their bodies producing antibodies that behave as if they’re TSH, causing their bodies to create too much thyroid hormone. The pituitary may also produce too little TSH, causing very low levels in the blood.
If the thyroid decreases the production of hormones, the individual can experience other symptoms, such as constipation, cold intolerance, fatigue, and dry skin. The most common cause of hypothyroidism in the United States is Hashimoto thyroiditis. This chronic autoimmune condition causes an immune response, which causes damage and inflammation in the thyroid while producing autoantibodies. The thyroid produces low levels of thyroid hormone, while the pituitary makes more TSH, leading to a very high level in the blood.
The level of TSH does not always accurately reflect the level of thyroid hormone levels, however. Some individuals create an abnormal form of TSH, which doesn’t work correctly. These individuals have hypothyroidism even though their TSH Thyroid-Stimulating Hormone levels are normal or possibly even slightly elevated. With many thyroid diseases, the hormone levels can be too high or too low, regardless of the amount of TSH present in the blood.
In some situations, pituitary dysfunction can cause decreased or increased amounts of TSH. Hyperthyroidism or hypothyroidism can happen if there is an issue with the hypothalamus, leading to insufficient or excessive TRH.
Typically, a TSH test is ordered along with a free T4 test. A free T3 test may also be ordered. It could also include a test of the levels of thyroid antibodies if any type of autoimmune-related thyroid disease is suspected. In some cases, numerous labs related to the thyroid are all ordered together as a thyroid panel.
Testing TSH can help doctors:
- Determine if a patient has a thyroid disorder
- Monitor anti-thyroid treatment in patients who have been diagnosed with hyperthyroidism
- Diagnose and monitor ongoing infertility issues in female patients, so that they can be treated appropriately
- Screen infants for an underactive thyroid so that treatment can begin as soon as possible
- Determine how well the pituitary gland is functioning overall
- Screen adults for thyroid disorders, although medical opinions vary as to when this screening should occur.
- Monitor thyroid replacement therapy in individuals who have been prescribed the therapy and diagnosed with hypothyroidism
When is This Test Ordered?
Healthcare providers can order a TSH test if someone has an enlarged thyroid gland, or if they have the symptoms of hypothyroidism or hyperthyroidism.
Signs and symptoms of hyperthyroidism can include:
- Increased heart rate with no other cause
- Ongoing anxiety that is not psychologically caused
- Unexplained weight loss
- Insomnia with no other cause
- Hand tremors with no neuromuscular cause
- Weakness in the body
- Occasional diarrhea
- Visual disturbances
- Sensitivity to Light
Ocular symptoms: Puffiness around the eyes, bulging eyes, dryness, and irritation.
Individuals who suffer from hypothyroidism can experience:
- Unexplained weight gain, not as a result of medications or diet
- Ongoing constipation
- Dry, flaky skin
- Cold intolerance
- Puffy skin
- Hair loss
- Irregular menstrual periods
TSH can be ordered at regular intervals when a patient is being treated for an existing thyroid disorder. The American Thyroid Association recommends waiting six to eight weeks after having thyroid medication adjusted before testing the level of TSH.
TSH screening is typically performed routinely in the United States on newborns as part of individual state’s newborn screening programs. This helps ensure that thyroid deficiencies are caught and treated early so that these individuals can lead healthy lives.
The U.S. Preventative Services Taskforce found insufficient evidence in 2004 to recommend either for or against regular screening at a specific age for adults with no symptoms. However, both the American Association of Clinical Endocrinologists and the American Thyroid Association released guidelines in 2012, suggesting that doctors consider screening patients older than 60 for hypothyroidism. The signs and symptoms of both hyperthyroidism and hypothyroidism are very similar to those of numerous other disorders. This makes it important for healthcare providers to rule out these diseases even if a patient has other health issues.
What Does the Test Result Mean?
A high TSH result can mean that:
The patient being tested has an underactive thyroid gland. The gland may not be functioning or responding to the stimulation of TSH. They may have thyroid dysfunction, either chronic or acute. Testing allows medical professionals to keep up with TSH levels and medication levels to help keep their patients healthy.
If a patient with hypothyroidism has their thyroid removed, their medication doses could be incorrect and may need to be adjusted. The same can be true of individuals with hyperthyroidism. These issues make medication monitoring and testing vital for these individuals. There is an issue with the pituitary gland, like a tumor, leading to unregulated production of TSH.
A low TSH result can indicate:
- An overactive thyroid gland
- Too much thyroid hormone medication in individuals who have had their thyroid gland removed or have an underactive thyroid gland. This makes it important to monitor medication levels carefully.
- Insufficient anti-thyroid medication in an individual who’s being treated for hyperthyroidism. It can take some time, however, for natural TSH production to resume after successful treatment. This is why the recommendation is that the treatment is monitored with tests for T4 and T3, as well as TSH levels.
- Damage to the pituitary gland that keeps it from producing enough TSH
- An abnormal TSH indicates that there is an issue with the amount of thyroid hormone available in the body, but it does not tell us why. An abnormal TSH test result typically requires additional testing to discover the cause of the increase or decrease.
What Else Should I Know?
It’s important to know that TSH, free T4, and free T3 test results are only a snapshot of what is happening within a dynamic system, and do not provide a healthcare professional with all the necessary information. Each individual’s thyroid test results can vary and can be affected by:
- Increases, decreases, and changes in the proteins that bind T3 and T4.
- Other Drugs
- Liver Disease
- System-Wide Illness
- Resistance to Thyroid Hormones
Many medications can affect the results of thyroid gland function tests, and it’s important to discuss their use with your doctor before the test itself. They can then advise you if you should take the medication on the day of the blood draw.
Illnesses that are not directly related to your thyroid – nonthyroidal illnesses – can still change the levels of thyroid hormones. The level of T3 can be low in nonthyroidal illnesses. Usually, the thyroid hormone levels go back to normal once the person has healed from the illness. This condition used to be called “euthyroid sick syndrome,” but this term has become controversial, as there is debate as to whether the thyroid functions normally (euthyroid).
If your doctor adjusts your thyroid hormone replacement dosage, it’s crucial to wait for at least a month or two before having the TSH level checked again, so that the new dose can fully take effect.
Acute illness and extreme stress can also affect TSH test results. It’s usually recommended that thyroid testing should be avoided in patients who are hospitalized or put off until you are well if you’re suffering from an acute illness.
Results can also be low during the first trimester of pregnancy.
Do Health Care Providers Test TSH During Pregnancy?
Healthcare providers don’t usually test women with no symptoms, but if a patient has symptoms or a thyroid disorder, they may be tested at specific intervals to detect or evaluate the thyroid disorder throughout the pregnancy and after.