The thyroid gland is a small gland in the front of the neck that is shaped like a butterfly. Although small in size, it regulates a number of metabolic and other bodily functions, including body temperature, energy level, heart rate, and many others. Too much or too little thyroid hormone can have a negative impact on one's overall health. Blood tests (thyroid function tests) can determine thyroid function. TSH, T3, and T4 are the three most commonly mentioned thyroid hormones and markers. These tests can enable individuals to pinpoint potential thyroid conditions and get medical advice if they need it. In Molecular Diagnostics and Therapy, diagnostic services for thyroid conditions are available to assist with the evaluation of thyroid conditions. Dr Nikunj Jain, an experienced specialist in Nuclear Medicine, is able to provide patients with guidance about further investigations of the thyroid depending on symptoms and clinical findings if these are needed. What Are Thyroid Function Tests? Blood tests known as thyroid function tests are used to check the normal regulation of thyroid hormones and to detect thyroid disorders. They can assist the doctor in assessing many conditions like an underactive thyroid gland (hypothyroidism) or an overactive thyroid gland (hyperthyroidism). Additional tests are also ordered to follow up those who are being treated for a thyroid problem. Which tests are chosen will be dependent on the symptoms displayed, medical history, medications, and history from earlier tests. The three important tests are: The three vital tests are:
TSH (Thyroid-Stimulating Hormone): Helps regulate thyroid hormone production.
T3 (Triiodothyronine): An active thyroid hormone involved in regulating metabolism.
T4 (Thyroxine): The main hormone produced by the thyroid gland, much of which can be converted into T3.
What Is a TSH Test?
Thyroid-stimulating hormone (TSH). It is made by a part of the brain called the pituitary gland. TSH prompts the thyroid gland to release and make thyroid hormones. TSH is ordered first to measure thyroid function because its level can be affected by variations in thyroid hormone levels. What Does a High TSH Level Mean? If your TSH level is elevated, this might be a sign that the thyroid is not making enough thyroid hormone. This is a typical reaction of hypothyroidism. Possible symptoms include:
Tiredness and low energy
Unexplained weight gain
Increased sensitivity to cold
Dry skin and hair changes
Constipation
Difficulty concentrating
But a high TSH level doesn't mean the cause. Other tests to help determine the condition may be recommended by your doctor, such as a free T4 test. What Does a Low TSH Level Mean? A low TSH level can mean the thyroid is producing excess hormone—generally a symptom of hyperthyroidism. Additionally, it can happen under other circumstances such as some pituitary problems or people who are taking high doses of thyroid hormone. Results must always be related to the individual and the symptoms and medical history. What Is a T3 Test? Triiodothyronine (T3) is a thyroid hormone that is important in regulating the body's metabolism. It plays a role in using the body's energy and helps to control the body's functions such as heart rate, temperature, and more. The thyroid produces a small amount of T3, but most is made when T4 is converted to T3 in other tissues. A T3 test may be used when your doctor thinks you may have hyperthyroidism, especially if your TSH is low and your free T4 is in the normal range. T3 may be raised in some forms of hyperthyroidism, sometimes before T4 rises, starting at an early age. What Do High and Low T3 Levels Indicate?
In some cases, T3 is increased with a normal T4 level and can be a sign of hyperthyroidism. Those who are very sick, have certain medical diseases, or have problems with nutrition may experience low T3. They also can exist during hypothyroidism; a decreased T3 level is not enough to diagnose an underactive thyroid. Depending on the clinical context, either total T3 testing or free T3 testing may be obtained. All of these tests measure the various forms of the hormone; therefore, they are not the same and don't interchange in every situation. What Is a T4 Test? The thyroid's most important hormone is T4 (also known as thyroxine). A T4 test can be used to check the levels of thyroid hormone. This test is often done in two forms: total T4 and free T4. Total T4 reflects both the bound to blood protein and free hormones. Free T4 (FT4): The available (unbound) hormone in the blood, which can enter into the body tissues. Free T4 is sometimes used in conjunction with TSH to evaluate thyroid function. What Do High and Low T4 Levels Mean?
If T4 is high, but TSH is low, in particular, then that may be a sign of hyperthyroidism. Some drugs and other clinical conditions can also lead to this. If the free T4 is low and the TSH is high, then primary hypothyroidism is most likely the cause. A low free T4 combined with either a low or normal TSH may necessitate more testing to rule out other potential causes of hypothyroid disease, such as problems with the pituitary gland and serious illness. A doctor evaluates all of the results and determines if treatment or more testing is needed. When Should You Get Thyroid Function Tests? Blood tests may be ordered to evaluate the thyroid when an individual's symptoms may be due to a thyroid disorder and/or when they have a medical history that raises a risk for a thyroid problem. If you have any of the following symptoms, then you might need to get a thyroid function test:
Persistent tiredness or unexplained weight changes
A fast or irregular heartbeat
Unusual sensitivity to heat or cold
Hair thinning or changes in skin texture
Changes in bowel habits
Menstrual irregularities
Swelling at the front of the neck
Unexplained anxiety, tremors or difficulty sleeping
Testing may also be recommended for people with a known thyroid condition who need treatment monitoring, those taking thyroid medication, or individuals with certain risk factors such as a family history of thyroid disease. Pregnancy and plans for pregnancy may also affect decisions about thyroid testing. The need for testing depends on individual circumstances and medical advice rather than symptoms alone. How Should You Prepare for a Thyroid Function Test? A blood test is usually taken for most thyroid function tests. For TSH, T3, and T4 tests alone, it is not necessary to fast, but if other tests are ordered simultaneously, follow your laboratory's directions. Always inform the doctor about any medication or supplements that you are taking prior to testing. There are some medications that may alter the results of thyroid hormone tests, or the interpretation of test results. Biotin, present in some hair, skin, and nail supplements, can interfere with some of the thyroid blood tests. Your doctor/lab might instruct you to stop using this for a while until the tests can be done. Never stop or change your thyroid medication without discussing it with your health care provider. Your doctor might want to check your blood at a particular time, depending on your medicine and why you are having blood tests. What Happens After the Test? Your doctor will reach a diagnosis when results are available based on the ranges the lab used as references, your medical symptoms, medicines that you've taken, and your medical history. If the tests indicate hypothyroidism or hyperthyroidism, other tests might be ordered to determine the cause. This includes checking for thyroid antibodies, physical examination, thyroid ultrasound, or, rarely, thyroid testing. Lab tests for the level of thyroid hormones are utilized to diagnose problems with the thyroid, and a scan of the thyroid, or nuclear medicine test, is used to determine the thyroid's uptake of the radioactive tracer. Not all tests are used for the same purpose; not all clinical settings use the same test.
Dr Nikunj Jain, a specialist in the field of nuclear medicine at Molecular Diagnostics and Therapy, can assist the patient in choosing the right nuclear medicine exams, if clinically indicated. The necessity for a thyroid scan will vary with the clinical question and be at the discretion of the doctor who is directly involved in the patient's care. Conclusion These blood tests provide information about thyroid function: TSH, T3, and T4. Usually, the first test ordered is TSH, and free T4 and free T3 tests are ordered to assess whether or not the thyroid is under- or overactive. No single result can be used to make a final decision, but when the trend of results is used, it can help doctors decide whether to conduct further testing or not. If symptoms are present or there is a personal history of thyroid disease, see a health professional who is knowledgeable about thyroid testing to see if testing is necessary. Rapid diagnosis may be helpful in the identification of thyroid disease and appropriate treatment.