Thyroid Function Test – Purpose, Procedure and Reading

The thyroid gland is an endocrine gland located in the lower front of your neck. It is responsible for creating thyroid hormones and carrying these to every tissue. Therefore, doctors rely on thyroid function tests to examine if your thyroid glands are in suitable condition and efficiently perform their duties.

Do you suffer from thyroid issues? Then, this article will give you a detailed guide regarding thyroid function tests!

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What Is a Thyroid Function Test?

Thyroid function tests constitute a standard series of blood tests useful in measuring the current performance of one’s thyroid gland. Commonly, tests such as TSH, T3RU, T4, and T3 are conducted in the healthcare sector. The thyroid gland has several responsibilities, including regulation of energy, mood and metabolism in the human body.

The purpose of conducting a thyroid function test is to examine the presence of thyroid disorders such as hypothyroidism and hyperthyroidism. If the report for a thyroid-stimulating hormone (TSH) or the T4 test comes abnormal, professionals might suggest additional tests to diagnose the exact problem.

What Is the Procedure of Performing a Thyroid Function Test?

When it comes to the procedure of a thyroid function test, the doctors rely on a simple blood drawing method. First, they will draw blood from your veins and store it in a small test tube. Then, they will send it for testing in a lab.

The following types of tests are commonly conducted for testing your thyroid gland.

Thyroid Stimulating Hormone (TSH): Produced in the pituitary gland, it regulates both T3 and T4 in the bloodstream.
Thyroxine: The T4 test is again responsible for analysing the presence of hypothyroidism and hyperthyroidism. Moreover, it is also used to monitor the treatment for thyroid disorders.
Free thyroxine: FT4 measures T4, which reduces the effects of protein naturally binding T4. It can prevent accurate measurement.
Triiodothyronine: A T3 test is again used to diagnose hyperthyroidism or the extent of hyperthyroidism. It is also used to manage the diagnosis or treatment of hyperthyroidism.
Free triiodothyronine: FT3 helps measure T3 in blood, which eliminates the effects of protein that naturally bind T3 and ultimately prevent accurate measurement.

How to Prepare for a Thyroid Test?

Usually, you do not need to prepare much for this test. However, if other blood tests are given alongside a thyroid test, your doctor might ask you to fast or prepare accordingly.

How to Read a Thyroid Function Test Report?

If you are curious about the interpretation of thyroid function test and its reading, it is mainly expressed in terms of the high or low presence of these hormones in the blood. The following table represents the average values of the thyroid function test.

Thyroid Test	Normal Range
Thyroid Stimulating Hormone	0.40-4.50 mIU/mL (milli-international units per litre of blood)
Thyroxine	5.0-11.0 ug/dL (micrograms per deciliter of blood)
Free thyroxine	0.9-1.7 ng/dL (nanograms per deciliter of blood)
Triiodothyronine	100-200 ng/dL (nanograms per deciliter of blood)
Free triiodothyronine	2.3-4.1 pg/mL (picograms per millilitre of blood)

Following this, a high level of T4, which is higher than 5.0-11.0 ug/dL, can cause hyperthyroidism. On the other hand, a TSH measure reading of more than 4.50 mIU/mL indicates a possibility of hypothyroidism. If your TSH is lower than 0.40 mIU/mL, you might face the risk of hyperthyroidism.

The doctors usually order a T3 test if your T4 and TSH tests suggest hyperthyroidism. If your T3 levels are abnormally higher than 100-200 ng/dL, it indicates that you might have a condition called Grave’s disease.

Do You Need to Take a Thyroid Test?

Now that you know what a thyroid test is, you must be wondering if you should take it. The thyroid gland produces two hormones, including triiodothyronine (T3) and thyroxine (T4). When it fails to produce these in your body, you will most likely suffer from hypothyroidism. On the other hand, you can also face hyperthyroidism if your thyroid produces excessive hormones. Its symptoms include the following.

Weight loss or gain
Lack of energy
Depression
Anxiety
Tremors
Sense of being on a high

If you face these symptoms in your body, you should visit the doctor immediately. They might suggest a thyroid test for this.

When to See a Doctor?

If your test reports fail to match the normal range of a thyroid function test, you must visit the healthcare centre. If the doctors find your thyroid gland overactive or underactive, they might suggest you go for an ultrasound test or a thyroid uptake test. These tests help find the exact problem by checking your thyroid gland activities and any tumours that might cause problems. They might also take samples from your thyroid tissues and check for cancer.

Now you know that taking a thyroid function test is essential for learning more about your thyroid gland and its hormones. Moreover, this test also helps you understand your possible health condition in the absence or overreaction of these hormones. Thus, doctors advise you to take this test immediately if you notice symptoms of thyroid-related diseases.

Frequently Asked Questions

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What is the leading cause of thyroid problems?

Generally, iodine deficiency and autoimmune diseases cause thyroid problems, causing hyperthyroidism.

Is there any standard medicine that interferes with thyroid function tests?

Among the common over-the-counter drugs, Biotin (Vitamin B7) supplements are capable of causing aberrancy in your thyroid function test. Therefore, you should avoid consuming it for about two days before such a test.