Thyroid is a butterfly-shaped small gland that is located in front of the neck. The wings of this gland wrap around the windpipe. Thyroid is one of the endocrine glands that release substances called ‘thyroxine’ hormone, also called the T4, and the T3 hormone directly into the bloodstream, and regulate the body’s metabolism- the chemical reaction that takes place inside body cells to convert food into energy for a variety of purposes from thinking to growth and development. Irregularities in T4 and T3 secretions could set off abnormal physical, mental, and emotional changes in the body.
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In the following article, we discuss the battery of tests that are available to assess thyroid functioning. However, it must be remembered that each case is unique and the prescribing doctor is the best person to recommend the right test to evaluate thyroid function.
Thyroid Function Tests (TFTs)
- TSH Tests – TSH is short for Thyroid Stimulating Hormone that is secreted by the pituitary gland. This controls the amount of thyroxine, or T4 hormone, produced by the thyroid gland. TSH blood test is usually the first step to determining changes in secretion of the hormone in blood. TSH levels is indirectly proportional to TH (Thyroid Hormone) levels in blood. A high TSH would mean low levels of TH, a condition called ‘hypothyroidism’, and low levels of TSH would mean surplus production of TH, a condition called ‘hyperthyroidism’. Additionally, a low TSH could also indicate an abnormal pituitary, which prevents it (TSH) from stimulating the thyroid – a condition called secondary hypothyroidism.
- T4 Tests – T4 stands for thyroxine and is the main thyroid hormone circulating in the blood. There are tests to measure bound and free T4 hormones in blood. A high TSH with low FT4 (free T4) or FTI (free T4 index) indicates primary ‘hypothyroidism’; conversely, a low TSH with an elevated FT4 or FTI would point to ‘hyperthyroidism’. A low TSH with a low FT4 or FTI would indicate ‘hypothyroidism’ that is induced by a problem with the TSH producing pituitary gland.
- T3 Tests – Such tests are normally recommended to diagnose hyperthyroidism or severity of the same. A hyperthyroid patient would show elevated levels of T3 in blood. Hypothyroid patients usually do not need T3 examination.
- Free T3 and Reverse T3 tests – Usually such tests are not clinically very useful. In healthy individuals, measurement of reverse T3 does not definitely determine whether hypothyroidism exists or not. Reverse T3 is an inactive protein which is structurally quite similar to T3 hormone.
- Thyroid Antibody Tests – Antibodies are produced by certain blood cells to fight infections during bacterial and viral attacks. However, in patients with hyper and hypothyroidism, lymphocytes make antibodies against thyroid cells. Hence, measuring levels of these thyroid antibodies could help assess the thyroid abnormality. Presence of anti-thyroglobulin antibodies indicate Hashimoto’s disease, and the TSI antibody or stimulatory TSH receptor antibody indicates Graves disease. Another antibody test is conducted to determine Graves disease – TSHR or TRAb.
- Non-blood Tests or Iodine Test – Radioactive Iodine Uptake (RAIU) is conducted on patients to determine how the radioactive iodine is used by the thyroid gland. This test helps measure the amount of radioactivity taken up by the gland. High RAIU is seen in hyperthyroidism, low RAIU is seen in hypothyroidism. Additionally, a thyroid scan is performed to ascertain what parts of the thyroid have taken up the iodine.
Let us also take a brief look at some types of medication that could interfere with the aforementioned Thyroid Function Tests:
- Estrogens – contraceptive pills, and drugs taken during pregnancy could indicate high levels of total T4 and T3. This is because estrogens present in these elevate the level of binding proteins.
- Biotin – Is an over-the-counter supplement taken to treat conditions like hair loss or ‘alopecia areata’. Typically, one must inform the treating doctor about the medication one is on before taking blood tests to determine thyroid functioning. A patient must be advised to stop taking biotin at least a couple of days before TFT, else the presence of the B vitamin supplement in blood could alter thyroid results.
Abnormal thyroid may be painless but has other serious health consequences like sudden weight loss or weight gain, course hair, frequent hair fall, hoarse voice, increased heartbeat, sleeplessness, anxiety, unexplained lethargy, irritability, erratic menstrual cycle, and more. Consulting a good thyroidologist is recommended. He would advise a series or combination of tests to diagnose the thyroid disorder and formulate a treatment plan.
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