- TSH (Thyroid-stimulating hormone) Test
- What is a TSH test?
- What is it used for?
- Why do I need a TSH test?
- What happens during a TSH test?
- Will I need to do anything to prepare for the test?
- Are there any risks to the test?
- What do the results mean?
- Is there anything else I need to know about a TSH test?
- TSH (Thyroid Stimulating Hormone) Test
- THIS DECISION WILL CHANGE YOUR LIFE, AS IT HAS FOR MANY OTHERS …
- Thyroid Function Tests
- Thyroid Blood Tests
- Thyroid Tests
- What blood tests do doctors use to check thyroid function?
- What imaging tests do doctors use to diagnose and find the cause of thyroid disease?
- What tests do doctors use if I have a thyroid nodule?
- What Your Hypothyroidism Test Results Mean
- Thyroxine, Triiodothyronine, and TSH Levels
- Hypothyroidism Tests: A Measure of Treatment Success
- How to Keep Hypothyroidism Under Control
TSH (Thyroid-stimulating hormone) Test
What is a TSH test?
TSH stands for thyroid stimulating hormone. A TSH test is a blood test that measures this hormone. The thyroid is a small, butterfly-shaped gland located near your throat. Your thyroid makes hormones that regulate the way your body uses energy. It also plays an important role in regulating your weight, body temperature, muscle strength, and even your mood. TSH is made in a gland in the brain called the pituitary. When thyroid levels in your body are low, the pituitary gland makes more TSH. When thyroid levels are high, the pituitary gland makes less TSH. TSH levels that are too high or too low can indicate your thyroid isn’t working correctly.
Other names: thyrotropin test
What is it used for?
A TSH test is used to find out how well the thyroid is working.
Why do I need a TSH test?
You may need a TSH test if you have symptoms of too much thyroid hormone in your blood (hyperthyroidism), or too little thyroid hormone (hypothyroidism).
Symptoms of hyperthyroidism, also known as overactive thyroid, include:
- Weight loss
- Tremors in the hands
- Increased heart rate
- Bulging of the eyes
- Difficulty sleeping
Symptoms of hypothyroidism, also known as underactive thyroid, include:
- Weight gain
- Hair loss
- Low tolerance for cold temperatures
- Irregular menstrual periods
What happens during a TSH test?
A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.
Will I need to do anything to prepare for the test?
You don’t need any special preparations for a TSH blood test. If your health care provider has ordered other blood tests, you may need to fast (not eat or drink) for several hours before the test. Your health care provider will let you know if there are any special instructions to follow.
Are there any risks to the test?
There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
What do the results 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. A TSH test does not explain why TSH levels are too high or too low. If your test results are abnormal, your health care provider will probably order additional tests to determine the cause of your thyroid problem. These tests may include:
- T4 thyroid hormone tests
- T3 thyroid hormone tests
- Tests to diagnose Graves’ disease, an autoimmune disease that causes hyperthyroidism
- Tests to diagnose Hashimoto’s thyroiditis, an autoimmune disease that causes hypothyroidism
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.
TSH (Thyroid Stimulating Hormone) Test
Your doctor may order a TSH test if you’re experiencing symptoms of a thyroid disorder. Thyroid diseases can be categorized as either hypothyroidism or hyperthyroidism.
Hypothyroidism is a condition in which the thyroid produces too few hormones, causing metabolism to slow down. The symptoms of hypothyroidism include fatigue, weakness, and difficulty concentrating. The following are some of the most common causes of hypothyroidism:
- Hashimoto’s disease is an autoimmune condition that causes the body to attack its own thyroid cells. As a result, the thyroid is unable to produce a sufficient amount of hormones. The condition doesn’t always cause symptoms, so it can progress over several years before it causes noticeable damage.
- Thyroiditis is an inflammation of the thyroid gland. It’s often caused by a viral infection or an autoimmune disorder, such as Hashimoto’s disease. This condition interferes with thyroid hormone production and eventually leads to hypothyroidism.
- Postpartum thyroiditis is a temporary form of thyroiditis that may develop in some women after childbirth.
- The thyroid uses iodine to produce hormones. An iodine deficiency can lead to hypothyroidism. Iodine deficiency is extremely rare in the United States due to the use of iodized salt. However, it’s more common in other regions of the world.
Hyperthyroidism is a condition in which the thyroid produces too many hormones, causing the metabolism to speed up. Symptoms of hyperthyroidism include increased appetite, anxiety, and difficulty sleeping. The following are some of the most common causes of hyperthyroidism:
- Graves’ disease is a common disorder in which the thyroid becomes larger and produces an excessive amount of hormones. The condition shares many of the same symptoms as hyperthyroidism and often contributes to the development of hyperthyroidism.
- Thyroiditis eventually leads to hypothyroidism, but in the short term, it can also trigger hyperthyroidism. This may occur when the inflammation causes the thyroid to produce too many hormones and release them all at once.
- Having too much iodine in the body can cause the thyroid to become overactive. This typically occurs as a result of continuously using medications that contain iodine. These medicines include some cough syrups as well as amiodarone, which is used to treat heart arrhythmias.
- Thyroid nodules are benign lumps that sometimes form on the thyroid. When these lumps begin to increase in size, they may become overactive and the thyroid may start producing too many hormones.
THIS DECISION WILL CHANGE YOUR LIFE, AS IT HAS FOR MANY OTHERS …
The Thyroid Jigsaw
Usual Normal Range
TSH – Thyroid Stimulating Hormone
0.5 – 4.00
T4 – Thyroxine Level
10 – 20
High End of Normal Range
|T3 – Triiodothyronine||Exactly in the middle of the range|
Thyroid Antibodies – TPO & TGO
4 – 8
Diagnoses for Graves’ and/or Hashimoto’s Diseases
It is not the fact that your Thyroid pathology result sits in the normal reference range, but where your result sits in the normal range!
Please Note: Reference ranges for children and pregnant women may vary from the normal adult reference range. Laboratory reference ranges can also vary. Always use the reference range as your guide in regard to the ATF recommendations for your best result and consult your thyroid treating doctor.
Thyroid Antibodies TPO & TGO – A positive result indicates Autoimmune Thyroid Disease, either Hashimoto’s or Graves’ Diseases.
Thyroid Ultrasound – An ultrasound of the thyroid shows the size, shape and texture of the thyroid gland and if nodules or cysts are detected in your thyroid gland. This test is an important as all the pathology tests. So if you have an enlargement of your thyroid gland or discomfort in your neck, a cough, or have trouble speaking or breathing, please speak to your doctor about ordering a thyroid ultrasound.
Additional Scan – Thyroid CT Scan – A Thyroid CT Scan is a Nuclear Medicine Scan. A small amount of radioactive iodine (RAI) contract solution is injected into the patient’s arm before the scan begins. The scan will show the update of the RAI Iodine through the Thyroid Gland.
Please Note: If your treating doctor has requested a Thyroid CT Scan and you have been diagnosed with Hyperthyroidism and/or a Heart Disorder, please be aware of related consequences from the RAI Contrast Solution used for CT Scans, MRI Scans and other Nuclear or Radiography Testing
Ref: Professor Jim Stockigt – ATF Thyroid News No 13, Sept 1999 – Iodine Contrast Solutions – Used in CT Scans and Other X-Rays.
Time to Have Pathology Tests?
Thyroid Pathology Tests should be done after fasting, as early as possible in the morning. Water can be consumed throughout the night, but nothing to eat after your evening meal.
Thyroxine Replacement Hormone, Oroxine, Eutroxsig and Eltroxin SHOULD NOT BE TAKEN BEFORE THE TEST. Take thyroxine after the test and wait at least 30 – 60 minutes before you eat breakfast. Taking Levothyroxine before the test, may indicate an incorrect result.
ATF MEDICATION TRAVEL PACK
The ATF Medication Travel Pack (MTP) is available for members of the organisation to purchase. The MTP will keep your thyroxine cool whilst away from home travelling or attending pathology appointments.
As medical science advances, we have more tests and biomarkers available to help identify illnesses. Yet overdiagnosis and overtreatment that may occur following abnormal results can cause dangerous adverse effects and costly consequences. Hypothyroidism — a lower than normal range of thyroid hormones — may be the poster child for this problem because it is such a common condition.
What is hypothyroidism?
At the front of your neck lies the thyroid, a butterfly-shaped gland that makes the hormone T4. When released into the bloodstream, T4 converts to T3, the most active form of thyroid hormone. Having sufficient levels of these hormones is important because the thyroid regulates body temperature, metabolism, blood pressure, and heart rate.
Hypothyroidism occurs when the thyroid is underactive (not working optimally). It affects as many as five in 100 people. Symptoms of hypothyroidism include fatigue, cold intolerance, constipation, dry skin, hair loss, muscle weakness, weight gain, and fertility problems.
In my primary care practice, I’m finding that more and more of my patients are reporting feeling tired and concerned about whether they have hypothyroidism. Some patients request many different thyroid blood tests to diagnose and treat hypothyroidism. But are these tests really necessary?
How is hypothyroidism diagnosed?
Most major medical associations recommended diagnosing hypothyroidism through a blood test using a simple two-step approach.
- First, we check the level of thyroid stimulating hormone (TSH), which the pituitary gland in the brain releases to stimulate thyroid hormone production.
- If TSH is high, we confirm low thyroid function with a test called free or unbound T4 (T4 in the bloodstream that is not attached to a protein).
It may help to think of the pituitary gland as a thermostat and the thyroid gland as a heater. The thermostat senses low temperatures outside of the body and turns on the internal heater. When body temperature reaches a set threshold, the thermostat signals the heater to stop working. In the body, it is the TSH produced by the pituitary gland that signals the thyroid to make more T4. When there is less free T4 in the blood, the pituitary senses the low levels and starts making more TSH.
Why not check thyroid hormones directly?
Why not check the thyroid hormones (T3 and T4) themselves, to see if the gland is not functioning properly?
The thyroid only makes small amounts of T3. Even in cases of severe hypothyroidism, T3 levels don’t go down that much. T4 is produced in large quantities by the thyroid. However, TSH is a far superior screening test because small changes in T4 cause large TSH spikes. Usually when a person has hypothyroidism, TSH levels become very high way before T4 levels fall below normal. So, in our analogy, the thermostat is very sensitive to small variations in temperature.
That’s why a normal TSH almost always means the thyroid gland is healthy and producing enough thyroid hormones. Research finds that a simple TSH test is enough to identify hypothyroidism in 99.6% of the tests performed.
You may have heard of expanded or full thyroid panels, which often include tests for TSH, total T3, total T4, free T3, free T4, anti-TPO antibodies, thyroglobulin, and reverse T3. There is no evidence these extra tests help to diagnose and manage thyroid disease, although they definitely add to health care costs. Proponents of expanded thyroid analysis believe more data may support a personalized intervention plan. However, what happens in a lab test often fails to mirror the elaborate dance of hormones in the body. Additionally, findings are highly variable. What happens in your body today may change in a matter of days or weeks, even without significant interventions.
How is hypothyroidism treated?
To make matters even more confusing, we still do not recommend universal treatment for people who have subclinical hypothyroidism: slightly elevated TSH (between 4.12 and 10 mU/mL) and normal free T4.
Even though subclinical hypothyroidism is associated with worse health outcomes, treatment with thyroid hormone medicine may not significantly improve a person’s symptoms and quality of life.
From my perspective, more lab testing may cause anxiety, generate further tests, and lead to unnecessary treatment, which can cost hundreds, and sometimes thousands, of dollars. We have good solid evidence to support simple tests to diagnose hypothyroidism and follow people who need treatment for it. I recommend questioning any doctors (and bloggers) who recommend tests that are not supported by clinical research. While it may sound like a good idea to check more biomarkers, it’s important to understand the limitations of weak evidence before embarking on this journey. On some of these websites, dollar signs are just a click away.
According to most guidelines, a TSH below 10 provides good reassurance that a person does not have hypothyroidism.
If you are diagnosed with subclinical hypothyroidism and you do not want to take thyroid hormones, it’s reasonable to recheck TSH and free T4 in two to three months to see if any changes have occurred.
If your main concern is your energy level, eating a healthy whole food diet, exercising more, reducing stress, and sleeping well can help. What’s more, this approach may improve many chronic health problems — and it certainly will not deplete your bank account.
Thyroid Function Tests
T4 and TSH results
The T4 test and the TSH test are the two most common thyroid function tests. They’re usually ordered together.
The T4 test is known as the thyroxine test. A high level of T4 indicates an overactive thyroid (hyperthyroidism). Symptoms include anxiety, unplanned weight loss, tremors, and diarrhea. Most of the T4 in your body is bound to protein. A small portion of T4 is not and this is called free T4. Free T4 is the form that is readily available for your body to use. Sometimes a free T4 level is also checked along with the T4 test.
The TSH test measures the level of thyroid-stimulating hormone in your blood. The TSH has a normal test range between 0.4 and 4.0 milli-international units of hormone per liter of blood (mIU/L).
If you show signs of hypothyroidism and have a TSH reading above 2.0 mIU/L, you’re at risk for progressing to hypothyroidism. Symptoms include weight gain, fatigue, depression, and brittle hair and fingernails. Your doctor will likely want to perform thyroid function tests at least every other year going forward. Your doctor may also decide to begin treating you with medications, such as levothyroxine, to ease your symptoms.
Both the T4 and TSH tests are routinely performed on newborn babies to identify a low-functioning thyroid gland. If left untreated, this condition, called congenital hypothyroidism, can lead to developmental disabilities.
The T3 test checks for levels of the hormone triiodothyronine. It’s usually ordered if T4 tests and TSH tests suggest hyperthyroidism. The T3 test may also be ordered if you’re showing signs of an overactive thyroid gland and your T4 and TSH aren’t elevated.
The normal range for the T3 is 100–200 nanograms of hormone per deciliter of blood (ng/dL). Abnormally high levels most commonly indicate a condition called Grave’s disease. This is an autoimmune disorder associated with hyperthyroidism.
T3 resin uptake results
A T3 resin uptake, also known as a T3RU, is a blood test that measures the binding capacity of a hormone called thyroxin-binding globulin (TBG). If your T3 level is elevated, your TBG binding capacity should be low.
Abnormally low levels of TBG often indicate a problem with the kidneys or with the body not getting enough protein. Abnormally high levels of TBG suggest high levels of estrogen in the body. High estrogen levels may be caused by pregnancy, eating estrogen-rich foods, obesity, or hormone replacement therapy.
Thyroid Blood Tests
What are thyroid blood tests and why are they taken?
Thyroid blood tests are used to tell if your thyroid gland is functioning properly by measuring the amount of thyroid hormones in your blood. They are done by withdrawing blood from a vein in your arm. These blood tests help to diagnose thyroid diseases.
The thyroid is a butterfly-shaped gland located in the front part of your neck. Its job is to produce thyroid hormones, which travel through your bloodstream and regulate many aspects of your body’s metabolism, including temperature, weight, and energy.
Thyroid blood tests show if you have:
- Hyperthyroidism: Overactive thyroid producing more thyroid hormones than your body needs. Hyperthyroidism speeds up your metabolism, which can cause weight loss, rapid heartbeat, insomnia, puffiness around the eyes, anxiety and other symptoms. The most common cause of hyperthyroidism is Graves’ disease.
- Hypothyroidism: Underactive thyroid producing too few thyroid hormones. Hypothyroidism slows down your metabolism, which can cause weight gain, menstrual irregularity, dry and puffy skin, fatigue and other symptoms. The most common cause of hypothyroidism is Hashimoto’s disease.
Thyroid blood tests are used to diagnose thyroid disorders associated with hyper- or hypothyroidism. These include:
- Graves’ disease.
- Hashimoto’s disease.
- Thyroid tumors.
- Thyroid nodule.
- Thyroid cancer.
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Health care professionals use thyroid tests to check how well your thyroid is working and to find the cause of problems such as hyperthyroidism or hypothyroidism. The thyroid is a small, butterfly-shaped gland in the front of your neck that makes two thyroid hormones: thyroxine (T4) and triiodothyronine (T3). Thyroid hormones control how the body uses energy, so they affect nearly every organ in your body, even your heart.
The thyroid is a small, butterfly-shaped gland in your neck.
Thyroid tests help health care professionals diagnose thyroid diseases such as
- hyperthyroidism—when thyroid hormone levels are too high
- Graves’ disease, the most common cause of hyperthyroidism
- hypothyroidism—when thyroid hormones levels are too low
- Hashimoto’s disease, of the most common cause of hypothyroidism
- thyroid nodules and thyroid cancer
Your doctor will start with blood tests and may also order imaging tests.
What blood tests do doctors use to check thyroid function?
Doctors may order one or more blood tests to check your thyroid function. Tests may include thyroid stimulating hormone (TSH), T4, T3, and thyroid antibody tests.
Thyroid blood tests check your thyroid function.
For these tests, a health care professional will draw blood from your arm and send it to a lab for testing. Your doctor will talk to you about your test results.
Health care professionals usually check the amount of TSH in your blood first. TSH is a hormone made in the pituitary gland that tells the thyroid how much T4 and T3 to make.
A high TSH level most often means you have hypothyroidism, or an underactive thyroid. This means that your thyroid isn’t making enough hormone. As a result, the pituitary keeps making and releasing TSH into your blood.
A low TSH level usually means you have hyperthyroidism, or an overactive thyroid. This means that your thyroid is making too much hormone, so the pituitary stops making and releasing TSH into your blood.
If the TSH test results are not normal, you will need at least one other test to help find the cause of the problem.
A high blood level of T4 may mean you have hyperthyroidism. A low level of T4 may mean you have hypothyroidism.
In some cases, high or low T4 levels may not mean you have thyroid problems. If you are pregnant or are taking oral contraceptives, your thyroid hormone levels will be higher. Severe illness or using corticosteroids—medicines to treat asthma, arthritis, skin conditions, and other health problems—can lower T4 levels. These conditions and medicines change the amount of proteins in your blood that “bind,” or attach, to T4. Bound T4 is kept in reserve in the blood until it’s needed. “Free” T4 is not bound to these proteins and is available to enter body tissues. Because changes in binding protein levels don’t affect free T4 levels, many healthcare professionals prefer to measure free T4.
If your health care professional thinks you may have hyperthyroidism even though your T4 level is normal, you may have a T3 test to confirm the diagnosis. Sometimes T4 is normal yet T3 is high, so measuring both T4 and T3 levels can be useful in diagnosing hyperthyroidism.
Thyroid antibody tests
Measuring levels of thyroid antibodies may help diagnose an autoimmune thyroid disorder such as Graves’ disease—the most common cause of hyperthyroidism—and Hashimoto’s disease—the most common cause of hypothyroidism. Thyroid antibodies are made when your immune system attacks the thyroid gland by mistake. Your health care professional may order thyroid antibody tests if the results of other blood tests suggest thyroid disease.
What imaging tests do doctors use to diagnose and find the cause of thyroid disease?
Your health care professional may order one or more imaging tests to diagnose and find the cause of thyroid disease. A trained technician usually does these tests in your doctor’s office, outpatient center, or hospital. A radiologist, a doctor who specializes in medical imaging, reviews the images and sends a report for your health care professional to discuss with you.
Ultrasound of the thyroid is most often used to look for, or more closely at, thyroid nodules. Thyroid nodules are lumps in your neck. Ultrasound can help your doctor tell if the nodules are more likely to be cancerous.
For an ultrasound, you will lie on an exam table and a technician will run a device called a transducer over your neck. The transducer bounces safe, painless sound waves off your neck to make pictures of your thyroid. The ultrasound usually takes around 30 minutes.
During an ultrasound, a transducer bounces sound waves off the neck to make images of the thyroid.
Health care professionals use a thyroid scan to look at the size, shape, and position of the thyroid gland. This test uses a small amount of radioactive iodine to help find the cause of hyperthyroidism and check for thyroid nodules. Your health care professional may ask you to avoid foods high in iodine, such as kelp, or medicines containing iodine for a week before the test.
For the scan, a technician injects a small amount of radioactive iodine or a similar substance into your vein. You also may swallow the substance in liquid or capsule form. The scan takes place 30 minutes after an injection, or up to 24 hours after you swallow the substance, so your thyroid has enough time to absorb it.
During the scan, you will lie on an exam table while a special camera takes pictures of your thyroid. The scan usually takes 30 minutes or less.
Thyroid nodules that make too much thyroid hormone show up clearly in the pictures. Radioactive iodine that shows up over the whole thyroid could mean you have Graves’ disease.
Even though only a small amount of radiation is needed for a thyroid scan and it is thought to be safe, you should not have this test if you are pregnant or breastfeeding.
Radioactive iodine uptake test
A radioactive iodine uptake test, also called a thyroid uptake test, can help check thyroid function and find the cause of hyperthyroidism. The thyroid “takes up” iodine from the blood to make thyroid hormones, which is why this is called an uptake test. Your health care professional may ask you to avoid foods high in iodine, such as kelp, or medicines containing iodine for a week before the test.
For this test, you will swallow a small amount of radioactive iodine in liquid or capsule form. During the test, you will sit in a chair while a technician places a device called a gamma probe in front of your neck, near your thyroid gland. The probe measures how much radioactive iodine your thyroid takes up from your blood. Measurements are often taken 4 to 6 hours after you swallow the radioactive iodine and again at 24 hours. The test takes only a few minutes.
If your thyroid collects a large amount of radioactive iodine, you may have Graves’ disease, or one or more nodules that make too much thyroid hormone. You may have this test at the same time as a thyroid scan.
Even though the test uses a small amount of radiation and is thought to be safe, you should not have this test if you are pregnant or breastfeeding.
What tests do doctors use if I have a thyroid nodule?
If your health care professional finds a nodule or lump in your neck during a physical exam or on thyroid imaging tests, you may have a fine needle aspiration biopsy to see if the lump is cancerous or noncancerous.
For this test, you will lie on an exam table and slightly bend your neck backward. A technician will clean your neck with an antiseptic and may use medicine to numb the area. An endocrinologist who treats people with endocrine gland problems like thyroid disease, or a specially trained radiologist, will place a needle through the skin and use ultrasound to guide the needle to the nodule. Small samples of tissue from the nodule will be sent to a lab for testing. This procedure usually takes less than 30 minutes. Your health care professional will talk with you about the test result when it is available.
What Your Hypothyroidism Test Results Mean
Results from a hypothyroidism blood test are the key to unlocking your best treatment plan. iStock
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If there’s a bright side to hypothyroidism, or an underactive thyroid, it’s that treatment usually just involves taking daily medication, and testing is limited to a simple blood test. Your hypothyroidism test results are your doctor’s blueprint for prescribing the right dose of synthetic thyroid hormone medication and tracking how well it’s working.
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 (TSH), 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. That’s 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 you’re making too little thyroid hormone, your TSH will go up. If you’re making too much thyroid hormone, your TSH will go down.”
What’s normal can vary depending on a number of factors, including the laboratory where your blood test is done, she adds. A normal range for TSH in most laboratories is 0.4 milliunits per liter (mU/L) to 4.0 mU/L.
If your TSH is higher than 4.0 mU/L on repeat tests, you probably have hypothyroidism.
Your doctor may also order a T4 test. Most of the T4 in your blood attaches to a protein, and when it does, it can’t get into your cells. Only T4 that is unattached or “free” can get into your cells to go to work. A blood test can measure how much free T4 if available.
Hypothyroidism Tests: A Measure of Treatment Success
Hypothyroidism is treated with daily medication. Taking synthetic thyroid hormone medication can bring your T4 and TSH levels back to their normal ranges. Once you’re on the right dose, your symptoms should subside.
When you first start taking medication, your doctor will need to monitor your blood to fine-tune the dosage. “Initially you will need to be tested more frequently,” Doria-Medina says. “A person who is newly diagnosed and taking medication for hypothyroidism should be tested every six weeks until the dosage is just right.”
The dose you start with is your doctor’s educated guess about what’s best for you — most likely the lowest dose possible to avoid side effects, which can include a rapid heartbeat and restlessness.
Medication for hypothyroidism is slow acting, and it can take several weeks for your body to adjust. If your TSH is still high and your symptoms haven’t subsided after 6 to 10 weeks, your doctor will likely increase the dose, and you’ll need your blood tested again after another 6 to 10 weeks.
How to Keep Hypothyroidism Under Control
Because you’ll 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 don’t 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 you’re 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 that’s 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 it’s ahead of schedule.
WHAT IS THE THYROID GLAND?
The thyroid gland is a butterfly-shaped endocrine gland that is normally located in the lower front of the neck. The thyroid’s job is to make thyroid hormones, which are secreted into the blood and then carried to every tissue in the body. Thyroid hormones help the body use energy, stay warm and keep the brain, heart, muscles, and other organs working as they should.
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 (T3) 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 (abbreviated TSH). 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 pituitary’s 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.
T4 and T3 circulate almost entirely bound to specific transport proteins. If the levels of these transport proteins changes, there can be changes in how much bound T4 and T3 is measured. This frequently happens during pregnancy and with the use of birth control pills. The “free” T4 or T3 is the hormone that is unbound and able to enter and affect the body tissues.
Blood tests to measure these hormones are readily available and widely used, but not all are useful in all situations. Tests to evaluate thyroid function include the following:
The best way to initially test thyroid function is to measure the TSH level in a blood sample. Changes in TSH can serve as an “early warning system” – often occurring before the actual level of thyroid hormones in the body becomes too high or too low. A high TSH level indicates that the thyroid gland is not making enough thyroid hormone (primary hypothyroidism). The opposite situation, in which the TSH level is low, usually indicates that the thyroid is producing too much thyroid hormone (hyperthyroidism). Occasionally, a low TSH may result from an abnormality in the pituitary gland, which prevents it from making enough TSH to stimulate the thyroid (secondary hypothyroidism). In most healthy individuals, a normal TSH value means that the thyroid is functioning properly.
T4 is the main form of thyroid hormone circulating in the blood. A Total T4 measures the bound and free hormone and can change when binding proteins differ (see above). A Free T4 measures what is not bound and able to enter and affect the body tissues. Tests measuring free T4 – either a free T4 (FT4) or free T4 index (FTI) – more accurately reflect how the thyroid gland is functioning when checked with a TSH.
The finding of an elevated TSH and low FT4 or FTI indicates primary hypothyroidism due to disease in the thyroid gland. A low TSH and low FT4 or FTI indicates hypothyroidism due to a problem involving the pituitary gland. A low TSH with an elevated FT4 or FTI is found in individuals who have hyperthyroidism.
T3 tests are often useful to diagnosis hyperthyroidism or to determine the severity of the hyperthyroidism. Patients who are hyperthyroid will have an elevated T3 level. In some individuals with a low TSH, only the T3 is elevated and the FT4 or FTI is normal. T3 testing rarely is helpful in the hypothyroid patient, since it is the last test to become abnormal. Patients can be severely hypothyroid with a high TSH and low FT4 or FTI, but have a normal T3.
Measurement of free T3 is possible, but is often not reliable and therefore not typically helpful.
Reverse T3 is a biologically inactive protein that is structurally very similar to T3, but the iodine atoms are placed in different locations, which makes it inactive. Some reverse T3 is produced normally in the body, but is then rapidly degraded. In healthy, non-hospitalized people, measurement of reverse T3 does not help determine whether hypothyroidism exists or not, and is not clinically useful.
THYROID ANTIBODY TESTS
The immune system of the body normally protects us from foreign invaders such as bacteria and viruses by destroying these invaders with substances called antibodies produced by blood cells known as lymphocytes. In many patients with hypothyroidism or hyperthyroidism, lymphocytes react against the thyroid (thyroid autoimmunity) and make antibodies against thyroid cell proteins. Two common antibodies are thyroid peroxidase antibody and thyroglobulin antibody. Measuring levels of thyroid antibodies may help diagnose the cause of the thyroid problem. For example, positive anti-thyroid peroxidase and/or anti-thyroglobulin antibodies in a patient with hypothyroidism result in a diagnosis of Hashimoto’s thyroiditis. While detecting antibodies is helpful in the initial diagnosis of hypothyroidism due to autoimmune thyroiditis, following their levels over time is not helpful in detecting the development of hypothyroidism or response to therapy. TSH and FT4 are what tell us about the actual thyroid function or levels.
A different antibody that may be positive in a patient with hyperthyroidism is the stimulatory TSH receptor antibody (TSI). This antibody causes the thyroid to be overactive in Graves’ Disease. If you have Graves’ disease, your doctor might also order a thyrotropin receptor antibody test (TSHR or TRAb), which detects both stimulating and blocking antibodies. Following antibody levels in Graves’ patients may help to assess response to treatment of hyperthyroidism, to determine when it is appropriate to discontinue antithyroid medication, and to assess the risk of passing antibodies to the fetus during pregnancy.
Thyroglobulin (Tg) is a protein produced by normal thyroid cells and thyroid cancer cells. It is not a measure of thyroid function and it does not diagnose thyroid cancer when the thyroid gland is still present. It is used most often in patients who have had surgery for thyroid cancer in order to monitor them after treatment. Tg is included in this brochure of thyroid function tests to communicate that, although measured frequently in certain scenarios and individuals, Tg is not a primary measure of thyroid hormone function.
RADIOACTIVE IODINE UPTAKE
Because T4 contains iodine, the thyroid gland must pull a large amount of iodine from the bloodstream in order to make an appropriate amount of T4. The thyroid has developed a very active mechanism for doing this. Therefore, this activity can be measured by having an individual swallow a small amount of iodine, which is radioactive. The radioactivity allows the doctor to track where the iodine goes. By measuring the amount of radioactivity that is taken up by the thyroid gland (radioactive iodine uptake, RAIU), doctors may determine whether the gland is functioning normally. A very high RAIU is seen in individuals whose thyroid gland is overactive (hyperthyroidism), while a low RAIU is seen when the thyroid gland is underactive (hypothyroidism). In addition to the radioactive iodine uptake, a thyroid scan may be obtained, which shows a picture of the thyroid gland and reveals what parts of the thyroid have taken up the iodine (see Thyroid Nodules brochure).
MEDICATIONS THAT INTERFERE WITH THYROID FUNCTION TESTING
There are many medications that can affect thyroid function testing. Some common examples include:
- Estrogens, such as in birth control pills, or in pregnancy, cause high levels of total T4 and T3. This is because estrogens increase the level of the binding proteins. In these situations, it is better to ask both for TSH and free T4 for thyroid evaluation, which will typically be in the normal range.
- Biotin, a commonly taken over-the-counter supplement, can cause the measurement of several thyroid function tests to appear abnormal, when they are in fact normal in the blood. Biotin should not be taken for 2 days before blood is drawn for thyroid function testing to avoid this effect.