When you go for a routine check-up, the one blood test that is commonly advised is the thyroid test.
Even if you have been having certain symptoms of thyroid disorder, your doctor will likely order this test to get a clear picture of your thyroid function. The results are your doctor’s blueprint for prescribing the right dose of medication and tracking how well the gland is working. These results can be difficult to understand on your own unless you are a medical expert. But don’t worry, we are here to clear up this confusion!
Keep reading to learn about the different types of thyroid tests, how they’re measured, and what your results really mean.
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First, Let’s Understand How The Thyroid Gland Functions.
The thyroid gland is a small endocrine gland of butterfly shape that sits in the front of your neck. The gland is stimulated or controlled by another endocrine gland present in the base of your brain called the pituitary gland. This little gland in your brain produces Thyroid Stimulating Hormone (TSH) which makes the thyroid produce the hormones thyroxine (T4) and triiodothyronine (T3) with the help of iodine that your body gets from the food you have.
T4 and T3 then travel to all your organs, and tissues via blood where they help with different bodily functions like maintaining heart rate, blood pressure, temperature sense, menstrual regularity, digestion, metabolism (the conversion of calories to energy), and help the organs work as they should.
The hormone that is secreted majorly by the thyroid gland is T4 (about 95%) which is an inactive form that freely circulates in the bloodstream and gets converted into active form, T3, in the liver and in certain other tissues.
As mentioned earlier, the production of these hormones is controlled by your pituitary gland. When the pituitary gland senses that your body has very little T4 it secretes more TSH to make the thyroid gland produce more. And when there are too many thyroid hormones in your blood circulation the pituitary gland makes less TSH. When the amount of T4 in your blood reaches a certain level, the pituitary gland shuts off the production of TSH.
This is how the mechanism works and the pituitary gland makes sure that your thyroid is always functioning right and producing a fairly constant amount of hormones. General physicians or Endocrinologists always advise a combination of TSH testing and thyroid hormone.
Understanding Thyroid Tests
TSH Test
A TSH test is a blood test that measures the level of TSH in your blood. Usually, TSH is the first hormone to be measured to check how well your thyroid is working. Changes in TSH levels can signal problems before thyroid hormone levels become abnormal.
High TSH Levels: This usually means your thyroid isn’t producing enough hormones, which is known as primary hypothyroidism or an underactive thyroid.
Low TSH Levels: This is a sign that your thyroid is overactive (hyperthyroidism). In rare cases, low TSH may occur if there’s an issue with the pituitary gland that prevents it from producing enough TSH, known as central hypothyroidism. In such a case, T4 is also measured.
T4 Test
The T4 test looks at total T4 and free T4. T
Total T4 is the entire amount of hormone that is present in your body. Free T4 is the amount of unbound hormone, not attached to another protein, which means it is in its active form and can enter tissues freely.
Free T4 is the important one to measure because it is the type that affects your body’s tissues.
If your Total T4 levels are abnormal, it may be due to medications or medical conditions affecting thyroid hormone-binding proteins. Factors like liver disease, oral contraceptives, and pregnancy, can increase these proteins, leading to higher Total T4 levels. Whereas, testosterone and anabolic steroids can decrease them, resulting in lower Total T4 levels.
Sometimes, during pregnancy, you may have normal thyroid function but your Total T4 could fall outside the usual range. Free T4 tests (either Free T4 or Free T4 Index) can give a more accurate picture of thyroid function in these cases.
T3 Test
T3 is the active thyroid hormone that is converted from T4. Similar to T4, T3 exists in both bound and unbound forms.
T3 blood tests include:
- Total T3: This measures the overall amount of T3 (both bound and unbound) in your bloodstream.
- Free T3: This indicates the amount of unbound T3 that is available for use by the body’s tissues.
- Reverse T3: This is an inactive form of T3 that does not have any biological function but can inhibit free T3 from entering tissues.
T3 levels are generally more useful for diagnosing an overactive thyroid (hyperthyroidism) rather than an underactive thyroid (hypothyroidism). In cases of hypothyroidism, T3 levels tend to be the last to show abnormal results. Additionally, since the level of free T3 in the body can be quite low, measuring it may be unreliable and less informative.
Thyroid Antibodies
In certain autoimmune conditions, your immune system may produce antibodies that target the thyroid gland. Primary types of antibodies include thyroglobulin antibodies (TgAb) and thyroid peroxidase antibodies (TPOAb). Testing for these antibodies can be useful in identifying the underlying causes of various thyroid disorders.
What is a Normal Thyroid Level?
To determine your thyroid hormone status, doctors use TSH and Free T4 tests. Normal ranges can differ slightly between laboratories, but typical ranges are:
TSH Normal Range: 0.5 to 5.0 mIU/L. However, in certain conditions—such as pregnancy, a history of thyroid cancer, previous pituitary gland issues, and older age—the TSH reference range is different and is compared with reference ranges advised by an endocrinologist.
Free T4 Normal Range: 0.7 to 1.9 ng/dL. People on medications affecting thyroid metabolism or those with thyroid or pituitary issues may need different target levels.
Total T4 Normal Range: 5.0 to 12.0 μg/dL.
Total T3 Normal Range: 80 to 220 ng/dL.
Free T3 tests are often not reliable and are generally not used for assessing thyroid function.
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What Does It Mean Your Thyroid Levels Are Abnormal?
When your thyroid lab results are abnormal, they can indicate different conditions based on the combination of TSH and thyroid hormone levels:
The following test results may indicate possible conditions:
- High TSH and low thyroid hormone levels indicate primary hypothyroidism.
- High TSH and normal thyroid hormone levels indicate subclinical hypothyroidism.
- Low TSH and high thyroid hormone levels indicate primary hyperthyroidism.
- Low TSH and normal thyroid hormone levels indicate early or mild hyperthyroidism.
- Low TSH and low thyroid hormone levels indicate pituitary disease.
- High TSH and low thyroid hormone levels indicate thyroiditis (thyroid inflammation).
The Bottom Line
Your thyroid is a key gland that helps control energy, metabolism, and growth in your body. Thyroid function tests can check how well your thyroid is working. These tests are useful if you already have a thyroid condition or if you’re dealing with new or unexplained symptoms. However, to get a clearer picture of the cause of thyroid disease it’s best to talk to your doctor. If you are diagnosed with one, Ayurvedic remedies like Krishna’s Thyro Balance Juice can help your gland balance hormone production naturally.
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