To accurately diagnose thyroid disorders and understand how thyroid hormones work in your body, a thyroid test is essential. Blood tests to measure thyroid hormones are readily available and widely used, but not all are helpful in all cases. Therefore, you may need special tests to assess thyroid function.
This article discusses the basics of thyroid testing and explains your options.
The importance of a thyroid test
The butterfly thyroid gland is the endocrine gland responsible for making calcitonin, thyroxine (T4), and triiodothyronine (T3). Research indicates that only T3 and T4 are the proper thyroid hormones produced by the thyroid gland. An imbalance in these hormones leads to many symptoms. For example, a chemical or hormonal imbalance arises when the thyroid gland produces too many hormones or does not produce enough hormones.
Symptoms of hypothyroidism are very common but non-specific, making it difficult to self-diagnose. Therefore, healthcare professionals rely on biochemical tests to confirm the presence of any potential thyroid disorder.
Thyroid tests can help diagnose thyroid conditions such as goiters, thyroiditis, and thyroid cancer and help your doctor better understand your condition. Measuring the level of thyroid antibodies helps diagnose an autoimmune thyroid disorder such as Graves’ disease. It is the most common cause of Hashimoto’s disease and hyperthyroidism. In addition, thyroid tests can help you determine the creation Hypothyroidism in newborns.
Thyroid function tests
Blood tests called thyroid function tests can detect an overactive or underactive thyroid gland. It can also provide information about other disorders associated with it. The most common tests of thyroid function are:
Thyroid stimulating hormone (TSH) test
The pituitary gland in the brain secretes a hormone called TSH, or thyroid-stimulating hormone. Your pituitary gland produces more TSH when your thyroid levels are low.
TSH tells the thyroid gland to adjust by releasing more thyroid hormones. Conversely, the pituitary gland produces less TSH when the thyroid hormone level is high. Therefore, excessively high or low TSH readings can indicate whether the thyroid gland is functioning properly.
A high TSH level indicates that the thyroid gland is underactive and not producing enough thyroid hormone. The opposite situation is when the TSH level is low, which means that the thyroid gland is producing too much thyroid hormone or is overactive. A normal TSH test result means that your thyroid gland is working properly.
The total T4 test measures the blood level (both bound and free) of the hormone T4. The free T4 test measures how much of the unbound hormone is free to enter and affect body tissues.
It is good practice for doctors to measure T4 in children, because T4 is essential for brain development. Tests that measure T4 more accurately reflect how the thyroid gland is functioning when examined with TSH.
Results showing elevated TSH but decreased free T4 (FT4) indicate primary hypothyroidism caused by any disease of the thyroid gland. On the other hand, low TSH and FT4 values indicate hypothyroidism due to a problem with the pituitary gland. Low TSH with elevated FT4 indicates the presence of hyperthyroidism.
The T3 test measures the other main thyroid hormone, T3 (triiodothyronine), in the blood. It is useful for diagnosing hyperthyroidism and determining the severity of your hyperthyroidism. This is because people with hyperthyroidism show an elevated level of T3. However, T3 testing is rarely useful in hypothyroid patients because they can have normal T3 with high TSH and low FT4.
Thyroid antibody test
The immune system produces thyroid antibodies, causing an autoimmune condition in the thyroid gland that results when these cells target and kill healthy thyroid cells.
While specific antibodies damage thyroid tissue and cause low thyroid hormone levels, other antibodies stimulate the thyroid gland to produce excessive thyroid hormones.
You can detect thyroid antibodies with a thyroid antibody test. Thyroid peroxidase, thyroglobulin, and thyroid hormone receptor antibodies are some of the most well-known thyroid antibodies.
When the thyroid gland produces too much or not enough hormones, it poses significant health risks. Therefore, thyroid tests are essential to understand how your body is doing in relation to thyroid hormone and antibody levels. While thyroid hormone levels can be determined by blood tests known as thyroid function tests, thyroid antibody tests detect different types of thyroid antibodies that cause autoimmune diseases.
When do you need to take the test?
The test is done when you have thyroid-related symptoms, or when your doctor has suspicions of an autoimmune thyroid disorder. Weight loss, anxiety, anger, sadness, hair loss, loss of menstruation or light are all indications of an overactive thyroid gland, which causes T3 and T4 levels to rise.
Lethargy, difficulty concentrating, weight gain, depression, excessive menstrual bleeding, and joint and muscle pain are all common signs of hypothyroidism (low levels of T3 and T4).
normal reference range
For any abnormal value, a doctor should be consulted. Depending on the results of your thyroid test, your hormone levels should normally fall between the following range:
- T3: 100-200 nanograms per deciliter of blood (ng/dL)
- T4: 4.5 – 11.2 micrograms per deciliter of blood (µg/dL)
- TSH: 0.4 – 5.0 milliinternational units per liter (mIU/dL)
- TSH (if you already have an underactive thyroid): 0.5 – 0.3 milliinternational units per liter (mIU/dL)
Preparation tips and precautions
- Usually, no additional precautions, such as fasting, are required before a thyroid test.
- Have your blood tested before taking your daily dose if you are already taking medication for thyroid disease.
- You can have a thyroid test during pregnancy if needed because thyroid changes are frequent during this time.
- Since taking biotin (vitamin B7) two days before a thyroid function test is known to cause some deviation in test results, it is best to avoid taking it.
The primary goal of thyroid tests is to diagnose thyroid disorders in the early stages. The test is vital because it is the most accurate way to diagnose and treat thyroid problems. In addition, test results can help your doctor develop an effective diagnosis and treatment plan. Talk to your doctor if you have questions or concerns about thyroid tests.