Thyroid Tests

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Your thyroid is a tiny glad, only about two inches in size, located in the upper part of your throat. It’s shaped like a pair of wings, with two nodes that sit on either side of your throat connected by a thinner band in the middle. This gland produces a hormone that is instrumental in controlling your metabolism.

Your thyroid produce two primary substances: thyroxine (T4) and triiodothyronine (T3). When your pituitary gland, located in your brain, senses your thyroid levels getting too low, it sends another hormone, thyroid-stimulating hormone (TSH), to your thyroid. This tells your thyroid to kick up the T4 and T3 levels again, keeping your metabolism moving.

Because your thyroid is what makes your metabolism work, it is connected to a number of different processes in the body. Your thyroid helps regulate your heart rate, your body temperature, and your brain function. When the thyroid isn’t working right, your entire body slows down.

There are two primary conditions that may require a thyroid test: hypothyroidism and hyperthyroidism. Hypothyroidism encompasses conditions in which your thyroid isn’t producing enough T3 and T4. Hyperthyroidism is the term for conditions where your body produces too much thyroid hormone.

Hypothyroidism, a condition when your thyroid isn’t making enough hormone, may be caused by , secondary hypothyroidism (a failure of the pituitary gland), or some inflammatory conditions. You may notice that you’re tired all the time, have trouble remembering things, gain weight, and feel cold all the time. You may also have dry skin, constipation, and general body weakness.

Hyperthyroidism, when your thyroid makes too much hormone, is often the result of a condition called If you have hyperthyroidism, you may notice that you have trouble sleeping, you’re nervous or irritable all the time, or you get hot easily. You may also have frequent diarrhea, trembling hands, a rapid heartbeat, and muscle weakness.

Thyroid blood tests are used to diagnose thyroid disorders associated with hyper- or hypothyroidism. These include:

TSH

One of the first things your doctor may test if you go to them with a thyroid complaint is your These are the levels of thyroid stimulating hormone in your blood, the hormone that tells your thyroid it’s go time. Your doctor will draw some blood to perform this test.

If your TSH levels are too high (above 4.0 mili-international units per liter), it may mean you have hypothyroidism. This may sound backward, but high TSH levels in your blood mean your thyroid isn’t absorbing the hormone properly. It never gets the signal to start producing thyroid hormone, your pituitary gland keeps dumping TSH into your blood, and those levels stay high.A TSH level below 0.4 milli-international units per liter might indicate hyperthyroidism.

Low TSH levels can mean your pituitary gland is getting signals that there is too much thyroid hormone in your blood. It stops sending out TSH in an attempt to get your thyroid to stop overproducing, so lower levels show up on your blood test.

T4 Free

T4 is one of the two primary hormones your thyroid produces. This hormone eventually gets converted to T3, which is the form of thyroid hormone that your body cells can absorb. T4 comes in two forms: , which enters body tissues where it’s needed, and bound T4, which is attached to proteins and can’t enter body tissues.

Levels of T4 higher than 12 micrograms per deciliter in your blood can mean your thyroid is producing more hormone than your body needs, indicating hyperthyroidism. Levels below 5 micrograms per deciliter can indicate that your thyroid isn’t producing enough, or you have hypothyroidism. The ratio of free to bound T4 can also give your doctor information about what your thyroid is doing.

T4 levels can vary for reasons other than a thyroid disorder. If you’re pregnant, you may see a fluctuation in either direction in your thyroid function. You may also see lower T4 levels if you’re taking corticosteroids or have a severe illness.

T3 Free

T3 is the other hormone your thyroid produces and the one T4 gets converted into later. This is the form that can be absorbed by receptor cells in the body and represents about 20 percent of the hormone your thyroid produces. This test is usually performed as a secondary test if TSH or T4 results come back abnormal.

If your bloodwork shows high levels of T4, your doctor may test your to make sure there isn’t something else causing the T4 elevation. They may also test your T3 even if your T4 levels are normal. If you’re still showing symptoms of hyperthyroidism even with normal T4 levels, you may have Grave’s disease.

If you have T3 levels above 200 nanograms per deciliter in your blood, you may have Grave’s disease or another form of hyperthyroidism. Levels below 100 nanograms per deciliter in combination with low T4 or high TSH levels could indicate hypothyroidism. T3 levels can also drop during a long illness, so bear that in mind.

T4 Total

In addition to testing for unbound T4, or free T4, you may also want to test your . This will include both free T4 and T4 that is bonded to protein in your body. T4 total tests may be ordered in conjunction with a number of other tests, including T3 and TSH, to help pinpoint what specific problem you may be dealing with.

Most of the T4 in your body is bonded to protein in your blood, so doctors prefer to perform a T4 free test because it takes a look at what is actually available for your body to use. But a T4 total test may help give your doctor a better picture of what's happening in your body that could be causing the change in T4 levels. T4 total levels may change with pregnancy or certain medication prescriptions, so be sure to look into that before you perform the test.

T3 Total

Like T4 total tests, look at both bound and unbound T3 hormones in your blood. This test is not ordered as commonly as the T3 free test because your body cannot use bound T3. But total T3 levels can help determine the severity of hypothyroidism or hyperthyroidism, as well as identifying T3 toxicosis.

T3 toxicosis is one of the conditions in which you have high levels of thyroid hormone in your blood. Running a T3 total test can help your doctor determine whether you're looking at T3 toxicosis or Grave's disease. As many as 11.7 percent of people with T3 toxicosis may not have Grave's disease, so it's important to know which group you fall into so you and your doctor can form an appropriate treatment plan.

T3 Reverse

Reverse T3, or rT3, is an inactive thyroid hormone produced when your body breaks down T4. Your body may start producing rT3 in greater quantities during times of sickness or starvation. It may be a mechanism to conserve energy during times when resources are slim.

People with hypothyroidism may have low levels of rT3 because overall thyroid hormone levels are low. RT3 levels below 250 pg/mL are considered to be within a normal range.

Thyroglobulin Antibodies

Your immune system makes a number of antibodies, agents that attack and destroy proteins that are not supposed to be in your body. When your body is exposed to diseases or other foreign materials, such as the flu or smallpox, it creates antibodies specifically equipped to fight that material. This is why vaccines work; your body encounters a deactivated form of the disease and can form the antibodies to fight it without you having to ever suffer the disease.

But sometimes your immune system starts creating antibodies to fight proteins like thyroglobulin, which are supposed to be in your body. A can take a look at levels of these antibodies in your blood; high levels can indicate an autoimmune problem.

Thyroid Peroxidase Antibodies

In several thyroid disorders, the immune system starts attacking the thyroid by mistake. Grave’s disease and Hashimoto’s thyroiditis are both examples of this kind of disorder. If your doctor believes you may have one of those conditions, they may run a thyroid antibody test.

Your doctor can run a blood test and see if there are detectable levels of antibodies against your own thyroid in your blood. If these antibodies are present, they can then use your TSH, T3, and T4 levels to diagnose you. In general, you want to see less than 35 international units per milliliterand less than 20 international units per milliliter of thyroglobulin antibody.

If you have normal levels of thyroid antibody but are still showing signs of hypothyroidism, you may yet have Hashimoto’s thyroiditis. The disease sometimes shows up as a nodule rather than as a diffuse goiter. In this case, antibodies may not show up, but you may still have symptoms.

TRAb

Thyrotropin receptor antibodies, like the other antibodies we mentioned, attack proteins that are supposed to be in your body. A TRAB test can help determine whether you have Grave's disease or not. But this test in particular can be very important for people who are pregnant.

High TRAb levels can indicate that a fetus may have a thyroid problem even before birth. Two in ten women with high TRAb levels during their third trimester have babies who are born with hyperthyroidism. Knowing this before your baby is ever born can help you and your doctors set up a treatment plan for your baby to make sure it gets the healthiest start in life possible.

TSI

Thyroid-stimulating immunoglobulin acts very much like TSH, but high levels in your bloodstream may indicate that you have Grave's disease. In some cases, TSI tests may be used to diagnose Hashimoto's thyroiditis and toxic multinodular goiter. When you have Grave's disease, your body starts mistakenly producing the antibody TSI. TSI levels below 130 percent are considered normal, but if your results are higher than 1.3, your doctor may want to run some additional tests.