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When And Why You Might Need A TSH Blood Test

Reviewed By: Dr. Kurt Kloss, MD
Last Reviewed Date: Sep 26, 2018
Last Modified Date: Sep 26, 2018
Published Date: Sep 24, 2018

The thyroid stimulating hormone, or TSH, is an important part of your endocrine system. This system includes your hypothalamus, pituitary gland, thyroid gland, parathyroid gland, adrenal glands, and more. TSH is one key part of proper functioning within this system. If your TSH levels are either too low or too high, it will clue your doctor in to issues with your thyroid gland that should be addressed.

You shouldn't ignore the signs and symptoms that will point you toward a TSH blood test. Getting this one simple test will give you valuable information for protecting your health. Read on to learn about what TSH does and how high and low TSH can impact your body. Understanding when you need to get a TSH blood test is important because diagnosing thyroid issues at the right time can save you from long-term complications.

What Is Thyroid Stimulating Hormone?

Image via Flickr by A W Dimmick

Thyroid stimulating hormone (TSH) is an important hormone released by the pituitary gland in the brain. This is one of many hormones involved with the thyroid. Thyroid hormone activity begins in the hypothalamus. The hypothalamus sits at the base of the brain, below the thalamus and above the pituitary gland. The hypothalamus produces TSH releasing hormone (TRH). As the name suggests, this hormone tells the pituitary gland to release TSH.

When TSH is released into the bloodstream, it prompts the thyroid gland to release its own hormones. The thyroid gland sits in the neck, around the trachea, and is shaped like a bowtie with a right lobe and left lobe connected by a narrow strip of tissue known as an isthmus in the middle. Some individuals do not have this isthmus and instead have two separate lobes.

If the brain determines that your thyroid levels are too low, it will release more TSH to boost the production of those hormones. If your body has too much of these hormones circulating in the bloodstream, the brain will reduce the amount of TSH that it produces.

There are two primary thyroid hormones that are impacted by the production of TSH — triiodothyronine (T3) and thyroxine (T4). T3 and T4 hormones travel throughout the body in the bloodstream. They're responsible for regulating several critical functions including your heart rate, body temperature, and cholesterol levels.

The thyroid also produces a hormone known as calcitonin. Made by c-cells in the thyroid gland, this hormone is related to your bone metabolism and helps regulate levels of calcium and phosphate. Calcitonin reduces calcium levels in the blood while the parathyroid hormone increases them. The role of calcitonin is relatively minor, and no major side effects have been noted with either low or high levels, so it's the other thyroid hormones that doctors primarily focus on when evaluating your TSH levels and how TSH is working in your body.

How Do Thyroid Hormones Work?

TSH is only one small part of the chain of hormones that are associated with the thyroid. TSH travels to the thyroid, but it is the T3 and T4 hormones that are actually produced by this gland. TSH is important to the overall process because of the messages that it communicates. When TSH reaches the thyroid, it binds to receptors on cells in the thyroid gland. These cells will then either increase or decrease their production of thyroid hormones.

Your body uses iodine to produce thyroid hormones. If it doesn't have enough iodine, it may not produce the proper levels of T3 and T4, despite the messages that it's receiving from the TSH. Your body cannot produce iodine on its own, so it must receive it from other sources. Your thyroid cells are the only ones in the body that can absorb iodine, so they have a monopoly on this commodity.

While iodine deficiency can cause thyroid problems, it's important to recognize that this is rare in the United States. Iodine is present in salt, bread, dietary supplements, and many water sources. The body needs 60 micrograms of iodine daily to produce thyroid hormones. In North America, the average iodine intake is 200 to 700 micrograms a day. Unless you're consuming a severely restrictive diet, you probably won't experience an iodine deficiency. This doesn't mean that you won't develop thyroid problems, only that iodine isn't likely the underlying cause of your issue.

What Do TSH Levels Tell You?

Your TSH level isn't a direct reflection of how much T3 and T4 your body has, because the thyroid gland doesn't necessarily produce as much of these hormones as the body is asking it to. Rather, your TSH levels are one piece of the puzzle that will help your healthcare provider get to the bottom of the issue if your thyroid hormones aren't where they should be.

If you have low thyroid hormones but high TSH, this indicates that the thyroid gland is underactive. Though it's receiving the message to make more T3 and T4, it's unable to do so. This is a condition known as hypothyroidism. When your TSH levels are high but your T3 and T4 levels are low, this indicates that your brain is signaling the thyroid gland to slow down its hormone production, but the gland is not responding properly. This condition is known as hyperthyroidism.

Your healthcare provider will often test your T3 and T4 levels with your TSH hormone. If T3 and T4 levels are not tested with your TSH levels, this test will be the next order of business should your TSH levels come back abnormal. You can't properly diagnose a thyroid problem unless you have information on all of these hormones.

A normal range for your TSH hormone is 0.4 to 4.0mIU/L (milli-international units per liter). If you're being treated for a thyroid disorder, your doctor will want to see these numbers in a smaller range, between 0.5 and 3.0mIU/L.

TSH levels are usually the opposite of your thyroid hormone levels. However, in some cases, you may find a low TSH level along with low T3 and T4 levels. This could be the result of a hypothalamic or pituitary process, severe euthyroid sick syndrome, or other problems. Your physician should examine several different aspects of your thyroid function before making a final diagnosis.

What Is Hypothyroidism?

Hypothyroidism is a condition in which the body doesn't produce enough T3 and T4 hormones. As mentioned previously, this is usually associated with a high TSH level because your brain is trying to tell the body that it needs more thyroid hormones. The body, however, is unable to respond due to an underactive thyroid. Hypothyroidism is particularly common in women over the age of 60.

When the thyroid gland is sluggish, your body also tends to be sluggish. It's not getting the hormones that it needs to signal your body to ramp things up. As a result, you may feel tired and worn down. Other symptoms of hypothyroidism include:

  • Constipation
  • Weight gain
  • Dry skin
  • Hoarseness
  • A puffy face
  • Muscle weakness
  • Aches, pains, and tenderness in the muscles
  • Thinning hair
  • Depression
  • Irregular or heavier menstrual periods
  • High cholesterol
  • Stiff, swollen, and painful joints
  • Slower heart rate
  • Sensitivity to the cold
  • Forgetfulness
  • Enlarged thyroid gland (goiter)
  • Decreased libido
  • Irritability
  • Memory loss

Left untreated, hypothyroidism can lead to more serious issues like heart disease or infertility. If hypothyroidism becomes advanced, you may experience myxedema. This is a life-threatening condition in which your body temperature and blood pressure become dangerously low. You may even slip into a coma.

If you're experiencing any symptoms of hypothyroidism, it's important to speak with your doctor. Testing your TSH, T3, and T4 levels can lead to a simple diagnosis. You may experience hypothyroidism for a number of reasons. One common cause of hypothyroidism is an autoimmune disorder known as Hashimoto's thyroiditis. With this condition, your body's own immune system produces antibodies that attack the thyroid gland. As a result, the thyroid gland becomes inflamed and the cells may become damaged.

You may also suffer from hypothyroidism if part of the thyroid is removed to treat other conditions, such as thyroid cancer. In some cases, treatments for hyperthyroidism overcompensate and leave the patient with an underactive thyroid instead. Fortunately, there are many treatment options for hypothyroidism, making this condition very easy to treat. The most important thing is getting the right tests and a clear diagnosis as early as possible.

What Is Hyperthyroidism?

Hyperthyroidism is the result of an overactive thyroid. This is what happens when the body slows production of TSH but the thyroid continues to produce hormones anyway. As a result, many of your body functions will go into overdrive, working harder than they should. Hyperthyroidism is most likely to occur in women. Your risk is higher if you've been pregnant in the last six months or if you're over the age of 60.

The symptoms of hyperthyroidism are generally the opposite of those associated with hypothyroidism. When you have hyperthyroidism, you might suffer from symptoms such as:

  • Unexpected weight loss
  • Increased appetite
  • Increased heart rate
  • Anxiety
  • Mood swings
  • Sweating
  • Tremors in the hands and fingers
  • Increased sensitivity to heat
  • Thinner skin
  • Brittle hair
  • Muscle weakness
  • Fatigue
  • More frequent bowel movements
  • Changes to the menstrual cycle
  • Goiter
  • Trouble sleeping

Hyperthyroidism is often misdiagnosed and associated with other conditions, such as menopause. Your physician may also miss a hyperthyroidism diagnosis due to other medications you're taking. If you use beta blockers, these will cover up some signs of hyperthyroidism, making it more difficult for your doctor to put the pieces together and get to the bottom of your issues.

A condition known as Graves' ophthalmopathy sometimes accompanies hyperthyroidism. Symptoms include red, swollen eyes or protruding eyeballs. You might experience sensitivity to light, blurry vision, and discomfort or tearing in one or both eyes. If you have trouble moving your eyes, experience double vision, or have any inflammation of the eyes, you may have this condition. Your risk for Graves' ophthalmopathy is higher if you smoke.

Hyperthyroidism is commonly caused by an autoimmune disorder known as Graves' disease. This stimulates your thyroid and causes it to produce too much T4. Some thyroid nodules can also cause your thyroid to overproduce T4. Inflammation of the thyroid gland for any reason can cause an excess of thyroid hormones to leak into your bloodstream. You shouldn't let hyperthyroidism go undiagnosed as it can lead to long-term issues like osteoporosis and heart problems.

What Indicators Let You Know You Need a TSH Test?

In general, you should take a TSH test any time you're experiencing symptoms associated with hyper- or hypothyroidism. This covers a very broad range of issues. You may have thyroid problems if you're either underweight or overweight. Both constipation and increased bowel movements are associated with various thyroid conditions. Trouble sleeping and irritability are associated with both hyper- and hypothyroidism. A goiter is another strong indicator of a thyroid problem. Your doctor may be able to identify an issue with your thyroid simply by feeling your neck.

For older women, a TSH screening may be a routine part of a general physical exam. Since thyroid problems aren't rare and may impact such a wide range of body systems, it's a good idea to include this in any set of tests if you're trying to diagnose a vague disease with many symptoms.

A TSH screening may also be a good idea for pregnant women. Thyroid changes during pregnancy can cause complications in some cases. Roughly one in 250 women experience hypothyroidism in pregnancy, while one in 500 experience hyperthyroidism. If you have either condition, it should be monitored carefully throughout your pregnancy so you can identify complications and other issues as early as possible.

How Does a TSH Blood Test Work?

A TSH blood test is very similar to other types of blood work that you may have done. There is no particular preparation that you need to go through before having a TSH blood test done. However, you should discuss all medication that you're taking with your doctor. Certain drugs may impact the results of your TSH test, so it's important for your healthcare provider to take these into account when evaluating your results.

Today's highly sensitive TSH tests can be used to diagnose thyroid issues before you're showing severe symptoms. It's possible that a TSH screening will clue you in about pending hypo- or hyperthyroidism even before your T3 and T4 levels have changed significantly.

If you are diagnosed with a thyroid condition, you will likely have many TSH tests done in the future. Your doctor will want to order another such test after a few weeks of treatment to determine its effectiveness. Close monitoring of your TSH, T3, and T4 levels is important so that you can properly manage your condition. The amount of medication that you need can change as your thyroid levels fluctuate. Fortunately, a TSH test is always quick and easy, requiring just a little bloodwork for accurate results.

What Happens After You Get TSH Blood Test Results?

A TSH blood test is only the first step in identifying thyroid issues. As mentioned previously, if you have this test performed alone, you will need to follow up by testing your T3 and T4 thyroid hormones once you get an abnormal result on your TSH screening. You're more likely to have an abnormal TSH with normal T3 and T4 levels than the opposite, which is why TSH is often tested first. Changes to TSH levels can be an early precursor to hyper- or hypothyroidism later on.

Once you've been diagnosed with hyper- or hypothyroidism, your doctor may go on to order further tests to diagnose either Graves' disease in cases of hyperthyroidism or Hashimoto's disease if you have hypothyroidism.

Though it can be frustrating to go through so many rounds of testing, it's important to recognize that these simple blood tests can give you a wealth of information about your health. After completing these tests, your doctor will have the necessary information to help you develop a personalized treatment plan that will restore your thyroid hormones to the proper levels.

Thyroid problems may seem to cause only minor discomforts for some, but both hyper- and hypothyroidism are dangerous when left untreated. With such simple treatment options, there's little reason not to pursue a solid diagnosis and long-term treatment.

What Can You Do for Hypothyroidism?

Hypothyroidism is typically treated with a synthetic thyroid hormone. Popular options include Levothroid and Synthroid. These are oral medications that you can take once a day to help increase your thyroid levels. It's best to take these pills at the same time every day, to provide your body with steady, ongoing access to the necessary hormones. If you allow your hormone levels to fluctuate, you're likely to feel the impact.

Hypothyroid treatments usually begin to take effect within about two weeks. One of the first changes that you'll notice is an increase in your energy levels. If you've gained weight as a result of the hypothyroidism, this excess weight may begin to melt away. Your cholesterol levels should drop and other symptoms will begin to reverse themselves.

Hypothyroidism is typically a lifelong condition. You'll need to stay on your medication indefinitely to supply your body with the proper level of thyroid hormones. Your doctor will check your hormone levels at least once a year and adjust your dosage as necessary. If you notice a recurrence of symptoms, you should contact your doctor to schedule another round of TSH, T3, and T4 testing as soon as possible. This will help you head off any more problems before they become too severe.

Avoid taking iron supplements, calcium supplements, certain antacids, and cholestyramine when you're taking levothyroxine. These interfere with your ability to absorb the medication. If you need these other supplements or medications, talk to your doctor about finding the right balance for your health.

You can also experience symptoms from having too high of a dosage. If your body increases its own output of thyroid hormones but you don't change the dosage of your medication, you'll suddenly have an excess of these hormones where you previously dealt with a deficit. Indicators that your medication dosage is too high include difficulty sleeping, heart palpitations, an increased appetite, and shakiness.

What Can You Do for Hyperthyroidism?

There are many different treatments that you might explore for hyperthyroidism. Beta blockers are one treatment that will help relieve some of the symptoms of hyperthyroidism quickly. You can begin feeling better within just a few hours of taking beta blockers. Antithyroid medications will address the underlying issue beneath your hyperthyroidism.

Antithyroid medications will help lower the levels of thyroid hormones in your body, but it may take months before your hormones are back in a healthy range. This is an ongoing treatment option. It does not cure your hyperthyroidism, but rather manages it. You will need to continue visiting your doctor for regular tests to see where your hormone levels are and adjust your dosage as needed.

Other treatments for hyperthyroidism are more permanent. However, these almost always result in hypothyroidism, which you must then control with medication as mentioned above. Radioiodine therapy is an oral treatment that destroys some of the body's thyroid-producing cells. For patients who cannot pursue other treatment options, thyroid surgery might be explored. This treatment involves removal of some or all of the thyroid.

In nearly any situation, you will require ongoing testing once you've been diagnosed with hyperthyroidism. You may struggle to maintain proper thyroid hormone levels throughout your life. By monitoring your TSH, T3, and T4 levels, your doctor can provide the best possible solution for your individual case, helping you balance these crucial hormones so you can stay healthy and comfortable.

Changes to your TSH levels can give you an early clue that there's something wrong with your thyroid. The earlier you can diagnose this problem, the less discomfort you'll ultimately suffer. Keeping your thyroid hormones balanced will support your heart health, reproductive health, and much more. If you think that you may need a TSH blood test, talk to your doctor about your symptoms now.