Thyroid Testing

The National Institute of Diabetes and Digestive and Kidney Diseases estimates that 4.6% of Americans aged 12 and older have hypothyroidism, also known as underactive thyroid. In people with hypothyroidism, the thyroid gland produces too little thyroid hormone. Hyperthyroidism is less common, with researchers estimating that it affects 1.3% of the U.S. population. In people with hyperthyroidism, the thyroid gland produces too much thyroid hormone.

This guide provides an overview of the thyroid panel, including what it measures and why it’s ordered. It also provides information on the causes, symptoms, risk factors, and treatment options for hypothyroidism and hyperthyroidism.

The purpose of the thyroid panel is to measure the levels of T3, T4, and TSH in an individual’s blood. High or low levels of these hormones can indicate that there’s a problem with the thyroid gland.

Experts from Harvard Medical School recommend that older women get the thyroid panel if they experience symptoms such as weight gain, fatigue, dry skin, difficulty thinking clearly, and cold hands. These symptoms are signs of hypothyroidism, but many women blame poor diet habits, a lack of exercise, or simply getting older instead of thinking that they might have a thyroid problem.

Based on guidelines issued by the American Academy of Family Physicians, the thyroid panel should also be performed when an individual has signs or symptoms of hyperthyroidism. Fast heart rate, weight loss despite normal appetite and eating habits, anxiety, and increased tear production are some of the symptoms of hyperthyroidism that indicate the need for thyroid tests.

The thyroid panel requires a small blood sample.

No special preparation is required for the thyroid panel, but the panel may be performed at the same time as other tests. Some of these tests, such as the lipid panel, require the individual to fast for nine to 12 hours before having blood drawn. Anyone scheduled for multiple blood tests should check with the ordering physician to find out if fasting is required.

Hypothyroidism has many potential causes, but the most common is a condition called thyroiditis. This condition causes swelling and inflammation of the thyroid gland, damaging the cells and resulting in impaired thyroid function. Thyroiditis sometimes develops in pregnant women; it can also be caused by viral infections and autoimmune diseases. In people with autoimmune diseases, the immune system attacks thyroid tissue as if it is a harmful substance. Hypothyroidism is also caused by some medications, radiation treatments used to treat head and neck cancers, thyroid surgery, certain birth defects, pituitary tumors or damage to the pituitary gland, and a condition called Sheehan syndrome, which occurs in pregnant women who experience severe bleeding.

Hypothyroidism causes a wide range of symptoms, some of which occur early on and others which develop only if the condition is left untreated. Some of the earliest symptoms include fatigue, constipation, joint or muscle pain, dry skin, weakness, paleness, brittle fingernails, thinning hair, and weight gain. Without treatment, hypothyroidism may eventually cause swelling of the face and hands, slow heart rate, hoarseness, low body temperature, reduced sense of taste, slow speech, thinning of the eyebrows, skin thickening, and reduced sense of smell.

The most common causes of hyperthyroidism include Graves disease and toxic multinodular goiter. Graves disease is an autoimmune disorder that causes the thyroid gland to produce too much thyroid hormone. Toxic multinodular goiter causes enlargement of the thyroid gland. In people with this condition, the thyroid gland has multiple nodules, at least one of which produces excess thyroid hormone. In pregnant women, a condition known as hyperemesis gravidarum can also cause hyperthyroidism. Hyperemesis gravidarum is characterized by excessive nausea and vomiting, which can lead to weight loss and dehydration. In rare cases, hyperthyroidism can be caused by tumors of the thyroid gland or pituitary gland.

Hyperthyroidism affects several body systems, producing a wide range of symptoms. Due to the effects of thyroid hormone on the nervous system, hyperthyroidism can cause fast heart rate, heart palpitations, anxiety, a “jittery” feeling, tremors, sweating, and inability to tolerate heat. Cardiovascular symptoms include difficulty breathing, irregular pulse, shortness of breath when lying down, and swelling in the arms or legs. Hyperthyroidism can cause the fingernails to separate from their nail beds. It can also cause hyperpigmentation of the skin, which is when some patches of skin become darker than the surrounding areas. Other symptoms of hyperthyroidism include difficulty sleeping, unexplained weight loss, light sensitivity, and rapid speech.

To collect a blood sample for a thyroid panel, a medical technician must insert a needle into one of the veins. This vein is usually behind the elbow or in the forearm, but blood can also be drawn from a vein in one of the hands. During a blood draw, the technician selects a vein, cleans the skin around the vein, and ties a tourniquet around the upper arm to make the vein more prominent. Once these steps are complete, the technician inserts a needle into the vein and collects a blood sample.

Levothyroxine is considered the “standard of care” for treating hypothyroidism. This medication acts as a replacement for the natural hormone that should be produced by the thyroid gland. People who take levothyroxine usually do so on an empty stomach, approximately one hour before eating the first meal of the day. It may take several weeks for levothyroxine to start working, so it’s normal to continue having symptoms until the body adjusts to the new medication. If a low dose of levothyroxine does not work, a health care provider may adjust the dose until the individual’s symptoms are under control and the results of a repeat thyroid panel are normal. Too much levothyroxine can cause symptoms similar to the ones produced by hyperthyroidism, including rapid weight loss, sweating, shaking, and heart palpitations, so it’s important to be monitored closely by a medical professional when making a dosage adjustment.

Hyperthyroidism is treated with beta-blockers, antithyroid medications, and ancillary agents. Beta-blockers slow down the heart rate and treat other symptoms of hyperthyroidism. Two of the most commonly prescribed beta-blockers for hyperthyroidism are atenolol and propranolol. For some people, atenolol is the safer of the two medications; atenolol is also much less expensive than propranolol.

Antithyroid medications prevent the thyroid gland from producing T3 and T4, relieving the symptoms of hyperthyroidism. Methimazole is often prescribed to treat hyperthyroidism, but it cannot be used during the first trimester of pregnancy. Women in their first trimesters can use propylthiouracil instead, but there is a higher risk of liver problems with this medication than there is with methimazole. Radioactive iodine is also used to treat hyperthyroidism, but it is not suitable for pregnant or nursing women. This treatment shrinks the thyroid so that it stops producing too much thyroid hormone.

Ancillary agents are used to reduce the amount of thyroid hormone circulating in the blood. Cholestyramine is a medication that binds with thyroid hormone so that it can be excreted from the body. Glucocorticoids can be used to treat severe hyperthyroidism by reducing the conversion of T4 to T3.

A normal TSH level ranges from 0.5 to 5 microunits per milliliter. Because TSH levels fluctuate throughout the day, it is best to have blood drawn early in the morning. Having blood drawn early in the day can also make it easier to fast for any other blood tests that have been ordered along with the thyroid panel.

A normal T3 result depends on whether the laboratory measures free T3 or total T3. Normal free T3 levels range from 0.2 to 0.5 nanograms per deciliter, while normal total T3 levels range from 75 to 195 nanograms per deciliter.

A normal free T4 level ranges from 0.8 to 2.8 nanograms per deciliter.

Some of the T3 and T4 produced by the thyroid gland goes directly into the tissues to be used right away. The rest binds with proteins, preventing it from entering the tissues — this is known as bound T3/bound T4. Total T3 includes free and bound T3, while total T4 includes free and bound T4.

Any blood draw has slight risks, including bleeding, bruising, and soreness at the needle insertion site. Some people may also get dizzy, sweat profusely, feel faint, or even pass out while having blood drawn.

Yes. Several medications can affect the results of a thyroid panel. Dopamine, glucocorticoids, opioids, and some chemotherapy drugs can reduce an individual’s TSH level. According to MedlinePlus, it may also be necessary to stop taking lithium, amiodarone, potassium iodide, and vitamin B-7 (biotin) before the test, as these medications can affect the TSH result. A diet high in iodine and the use of thyroid medications can affect the results of the free T3 test. Phenobarbital can affect the results of the free T4 test. Because medications can affect the results of the thyroid panel, it is important to tell a health professional about any prescription medications, over-the-counter medications, or supplements.

More tests may be needed depending on an individual’s symptoms and whether the ordering physician believes additional testing is necessary. If a health care provider suspects that an autoimmune disease is causing thyroid-related symptoms, a blood test for antithyroid antibodies can provide valuable diagnostic information. These antibodies attack the thyroid gland, causing damage that can lead to hypothyroidism or hyperthyroidism. A health care provider may also decide to order imaging tests to look for thyroid nodules or determine the cause of an individual’s hyperthyroidism. One of the imaging tests used to find the cause of hyperthyroidism is the thyroid scan, which uses a radioactive substance to create an image of the thyroid gland. This image helps medical professionals determine if the thyroid is enlarged or whether it has any nodules that could be interfering with the function of the gland.

For more information about hypothyroidism and hyperthyroidism, and the tests used to diagnose and monitor these conditions, visit these resources.

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