The thyroid gland is a butterfly-shaped organ located in the front of your neck.
The thyroid produces thyroid hormone, which is vital for proper metabolism, body
temperature regulation and support for all of your organs. When your thyroid does not
function properly, you may experience a range of symptoms, such as intolerance to
cold, heart arrhythmias, fatigue, hair loss and enlargement of the thyroid gland itself.
According to the American Thyroid Association, your doctor can order the following
blood tests to verify that your thyroid is functioning properly.
The thyroid gland produces a major hormone called thyroxine, or T4, which is vital
to your health because other hormones rely greatly on sufficient thyroxine levels. The
amount of T4 produced depends on a hormone produced in the pituitary gland called
thyroid stimulating hormone, or TSH. The pituitary gland, located at the base of your
brain, determines how much TSH to release based on how much thyroxine is detected.
When your level of T4 is low, the pituitary gland releases more TSH. When your T4
level is high, production of TSH is shut off by your pituitary gland. Because TSH is so
vital for proper thyroid function, it is often the first test ordered when thyroid function
is questioned. A low level of TSH indicates that you may have an overactive thyroid,
resulting in a condition called hyperthyroidism. However, a high level of TSH indicates
that you may have an underactive thyroid, known as hypothyroidism. Both conditions
require medical attention and should be treated by your doctor.
As mentioned before, the major hormone secreted by your thyroid gland is T4. There
are two forms of T4, but free T4 is considered the most important value because this
number represents the amount of free T4 circulating in your bloodstream. You may see
this on your lab test as Free T4 (FT4) or Free T4 Index (FT4I or FTI), depending on the
lab. Your T4 level helps your doctor evaluate if the hormone is reaching the tissues in
your body that need thyroid hormone to function properly. To accurately evaluate thyroid
health, your doctor will consider both your TSH level and T4 level to make an accurate
diagnosis. An elevated TSH level with a low T4 level indicates primary hypothyroidism,
often because of thyroid gland disease. However, a low TSH level coupled with a low T4
level indicates hypothyroidism due to a malfunctioning pituitary gland. In addition, a low
TSH level with a high T4 level often signifies an overactive thyroid.
T3 tests are helpful for diagnosing the extent of thyroid disease, and are especially
helpful for evaluating hyperthyroidism. This is because people with an overactive thyroid
often have a high T3 level due to the nature of the disease. In fact, other lab values may
be normal in people with hyperthyroidism. However, the T3 level is almost always
elevated with hyperthyroidism, making it a useful tool for diagnosing overactive thyroid
conditions. T3 levels are usually not very helpful for diagnosing hypothyroidism because
it is usually the last test to show changes related to underactive thyroid disorders.
Thyroid Antibody Tests
Although TSH, T4 and T3 levels help your doctor diagnose thyroid disease, thyroid
antibody tests help your doctor determine the cause of your thyroid disease, especially
if the blame is your immune system. You may wonder how your immune system has
anything to do with your thyroid, but the immune system is responsible for many cases
of hyperthyroidism and hypothyroidism. Your immune system makes antibodies called
lymphocytes, which help protect your body from germs, viruses and other foreign
invaders. However, these immune cells can also produce antibodies that stimulate or
damage the thyroid gland. By measuring these antibodies, your doctor can determine
if your thyroid disease is autoimmune in nature, meaning the immune system has
mistakenly attacked your thyroid gland. A positive antibody result is called autoimmune
thyroid disease in a hypothyroid patient and Hashimoto’s thyroiditis in hyperthyroid
patients. Both conditions are treatable with prescription medications.