I. Overview of the TSH Test

Why should I get tested?

The purpose of the TSH test is to determine if an individual has a higher-than-normal TSH level or a lower-than-normal TSH level. A high TSH level is a sign of an underactive thyroid, while a low TSH level is a sign of an overactive thyroid. The TSH test is helpful for diagnosing thyroid problems and monitoring the effects of medications and other treatments.

When should I get tested?

According to MedlinePlus, a TSH test should be ordered when an individual has symptoms of either hypothyroidism or hyperthyroidism. Hypothyroidism can cause symptoms such as weight gain, fatigue, and hair loss, while hyperthyroidism can cause weight loss, increased heart rate, and difficulty sleeping. Dr. Michael Sheehan advises against ordering the TSH test for every patient, as many of the symptoms caused by hypothyroidism and hyperthyroidism can also be caused by other medical conditions. Therefore, the test should only be ordered for people showing symptoms of a thyroid disorder.

What is required for the test?

The TSH test is performed on a small sample of blood.

What do I need to do to prepare for the test?

The TSH test doesn’t require any special preparation, but it’s often performed at the same time as other blood tests. Food and beverages can affect some test results, so it may be necessary to fast overnight before having blood drawn.

II. The Basics of Hypothyroidism and Hyperthyroidism


In people with hypothyroidism, the thyroid gland doesn’t produce enough of the hormones needed to regulate metabolism, control heart rate, and carry out other important functions. Without enough thyroid hormone, some of the body’s functions are sluggish. For example, many people with hypothyroidism gain weight because they don’t have enough thyroid hormone to maintain a normal metabolic rate.

Several risk factors increase the risk of developing. People with a history of thyroid problems, those who have had thyroid surgery or radiation treatment of the thyroid, and people with a family history of thyroid problems are more likely to develop hypothyroidism than others. The presence of certain medical conditions also increases the risk of hypothyroidism. For example, people with Sjogren’s syndrome, lupus, rheumatoid arthritis, and Type 1 diabetes have an increased risk of developing an underactive thyroid. Hypothyroidism is also more common in women and adults over the age of 60.

The most common cause of hypothyroidism is a condition called thyroiditis. In people with this condition, inflammation damages the thyroid gland, impairing its ability to produce enough thyroid hormone. Because the pituitary gland produces TSH, the hormone that stimulates the thyroid gland to produce hormones, damage to the pituitary gland may also cause hypothyroidism.

Not everyone with hypothyroidism experiences the same symptoms, but fatigue, weight gain, and thinning hair are common. Hypothyroidism can also cause depression, puffiness of the face, fertility problems, a slower heart rate, joint pain, muscle pain, intolerance to cold, menstrual irregularities, and decreased sweating. Some people with hypothyroidism also develop goiter, an enlargement of the thyroid gland that may be accompanied by the development of nodules in the thyroid.


In people with hyperthyroidism, the thyroid gland makes too much thyroid hormone, speeding up certain body functions. For example, people with hyperthyroidism are likely to have a faster-than-normal heart rate or lose weight without trying due to an increase in their metabolic rate.

A family history of thyroid disease is one of the risk factors for hyperthyroidism. An individual’s personal health history can also influence his or her risk of developing this condition. People with Type 1 diabetes, a hormonal disorder called primary adrenal insufficiency, and a B-12 deficiency known as pernicious anemia all have a heightened risk of developing hyperthyroidism. Since iodine affects thyroid function, eating a lot of iodine-rich foods or taking medications that contain iodine can also increase the risk of developing an overactive thyroid. Women and adults over the age of 60 are more likely to develop hyperthyroidism than men and adults under the age of 60.

Symptoms of hyperthyroidism include fast heartbeat, irregular heartbeat, anxiety, nervousness, shaky hands, difficulty sleeping, heat intolerance, mood swings, weight loss, and muscle weakness. Left untreated, hyperthyroidism can cause serious complications. For example, an irregular heartbeat caused by hyperthyroidism can cause clots to form in the blood vessels, triggering a stroke. Hyperthyroidism can also lead to osteoporosis or an eye condition that causes light sensitivity and double vision.

III. How a TSH Test Works

To determine how much TSH is in the blood, an individual must provide a blood sample. Although blood draws are often performed in medical clinics and outpatient laboratories, some companies now offer home test kits. With a home test kit, it’s possible to collect a blood sample in a comfortable environment instead of having to drive to a draw site and wait in line to have blood drawn by a phlebotomist.

TSH is measured using a laboratory procedure known as a microparticle enzyme immunoassay. During this procedure, laboratory personnel add the patient’s blood sample to antibody-coated microparticles, allowing the microparticles, antibodies, and blood to bind together. A second antibody is labeled with an enzyme and added to the mixture. Laboratory personnel then use an enzyme substrate to trigger a chemical reaction. The product of that reaction is measured in terms of fluorescence or color absorption, making it possible to quantify the amount of TSH present.

IV. Treatment for Hypothyroidism and Hyperthyroidism


The most common treatment for hypothyroidism is levothyroxine, a synthetic form of thyroid hormone. Levothyroxine acts as a replacement for natural thyroid hormone, relieving the symptoms of hypothyroidism. An individual with hypothyroidism typically takes a low dose of levothyroxine at first, as starting out at a low dose can limit side effects. If a repeat TSH test shows that the thyroid gland is still underactive, the dose can be increased. It’s important for an individual with hypothyroidism to be monitored closely after a dosage increase; too much levothyroxine can speed up the heart rate and produce other symptoms associated with an overactive thyroid gland.


Antithyroid medications are typically used to treat hyperthyroidism. These medications reduce the amount of thyroid hormone produced by the thyroid gland, relieving symptoms such as fast heart rate, rapid weight loss, anxiety, and heat intolerance. It’s important for pregnant and nursing women to work closely with their healthcare providers to find a treatment for hyperthyroidism that’s also safe for a developing fetus or nursing baby. Some antithyroid medications are not safe to take during pregnancy or while breastfeeding.

Some people also take cholestyramine, a medication that increases the excretion of thyroid hormone. Rather than stopping the thyroid from producing thyroid hormones, cholestyramine binds with the hormones so they can be eliminated in the feces. Beta-blockers are also used in the treatment of hyperthyroidism. These medications slow down the heart rate, reducing the risk of stroke and other heart-related complications.


What is a normal TSH level?

A normal TSH level ranges from 0.4 to 5.5 milli-international units per milliliter (mU/mL) of blood.

Which hormones does the thyroid gland produce?

The thyroid gland produces triiodothyronine (T3) and thyroxine (T4). T3 and T4 work together to regulate metabolism, heart rate, respiratory rate, cholesterol level, weight, body temperature, menstruation, brain development, nervous system function, and the amount of moisture in the skin.

Can hypothyroidism cause any complications?

Yes. If left untreated, hypothyroidism may lead to high cholesterol, infertility, nerve damage, and depression. People with large goiters may have difficulty breathing or swallowing normally. In pregnant women, untreated hypothyroidism has also been linked to miscarriages, premature births, and children born with birth defects.

Can hyperthyroidism cause any complications?

Yes. Untreated hyperthyroidism puts a lot of stress on the body, increasing the risk for problems such as abnormal heart rhythms and heart failure. Some people with hyperthyroidism may also experience a complication known as thyrotoxic crisis, which causes delirium, rapid heart rate, and fever. Thyrotoxic crisis requires immediate medical attention.

If my TSH is too high or too low, will I need additional tests?

If an individual’s TSH is too high or too low, a healthcare provider is likely to order a full thyroid panel, which also measures T3 and T4 levels. Thyroid antibody tests may also be ordered if there’s any indication that an individual’s symptoms are caused by an autoimmune disease. In people with autoimmune diseases, the immune system attacks healthy tissue, causing permanent damage. Some autoimmune diseases target the thyroid gland, resulting in the destruction of thyroid tissue. For example, Graves’ disease attacks the thyroid, causing it to produce too much T3 and T4. This overproduction of thyroid hormones leads to symptoms such as rapid heart rate, anxiety, and sweating.

Graves’ disease has many of the same symptoms as hyperthyroidism, but it can also cause diarrhea and frequent bowel movements. Left untreated, Graves’ disease can cause serious complications, including Graves’ ophthalmopathy, an eye condition that can cause blurred vision, double vision, and increased sensitivity to light. People with other autoimmune disorders, such as lupus and rheumatoid arthritis, have a heightened risk of developing Graves’ disease.

VI. Additional Resources

For more information on hypothyroidism and hyperthyroidism, along with testing for each condition, use the following resources.

Name Website Summary
American Thyroid Association www.thyroid.org The American Thyroid Association offers in-depth information on medical conditions affecting the thyroid gland.
National Institute of Diabetes and Digestive and Kidney Diseases www.niddk.nih.gov Learn more about hypothyroidism and hyperthyroidism, including how common they are and what can happen if they aren’t treated.
MedlinePlus www.medlineplus.gov Find out more about TSH testing, as well as tests to measure the amounts of T3 and T4 in the blood.
Graves’ Disease and Thyroid Foundation www.gdatf.org The Graves’ Disease and Thyroid Foundation provides information on Graves’ disease, an autoimmune disorder that can damage the thyroid gland.
The Magic Foundation www.magicfoundation.org Learn more about congenital disorders that can cause thyroid problems.
Merck Manuals www.merckmanuals.com Access educational materials about hypothyroidism and hyperthyroidism.

VII. Sources Used in This Article