What Is A Full Thyroid Test?

What Is A Full Thyroid Test?

Phlebotomy procedure during coronavirus crisis. medical worker preparing to take blood for analysis
Dr. Natalie Bessom
Medically reviewed by

Natalie Bessom, D.O. Board-certified family medicine doctor with specialty training in nutrition, USA

Learn what a full thyroid test looks like, the importance of each test, what to expect during a full thyroid test, and aftercare. 

In this article:

Your thyroid is a small butterfly-shaped gland located at the front of your neck that produces and regulates hormones that manage your body’s metabolism, heartbeat, temperature, mood, and more. 

When your thyroid produces too little (hypothyroidism) or too much (hyperthyroidism) hormones your entire system and bodily functions will be affected. 

What is a full thyroid test?

A thyroid blood test measures your thyroid function. The most common test that is conducted only measures your TSH (Thyroid-stimulating hormone). Unfortunately, testing TSH alone is not able to provide a full picture of your thyroid health even though it is the most common test conducted by clinicians. 

 A full thyroid test should include testing the following, depending on your health circumstances: 

  • TSH
  • T3 (triiodothyronine) Test
  • T4 (thyroxine) Test
  • TPO Antibodies
  • Reverse T3
  • Tg (Thyroglobulin)
  • Tg Antibody (TgAB)

Each test offers a different piece of information regarding your thyroid. Together they provide a holistic view of your full thyroid health. 

What is so important about each test and what are the differences?

TSH (Thyroid-stimulation hormone)

The initial and most widely used test measures the level of TSH. Changes in your body’s TSH level can be seen as an “early warning system”as they may occur before the actual levels of thyroid hormones are seen too high or too low. TSH is mainly used to regulate the amount of thyroid hormones – T3 (triiodothyronine) and T4 (thyroxine) that is produced by the thyroid gland. 

A high level of TSH indicates that your thyroid gland is not producing enough thyroid hormones (hypothyroidism). A low level of TSH indicates that your thyroid gland is producing too much thyroid hormone and is classified as hyperthyroidism. 

While TSH is the standard test that more clinicians will provide, it only provides insight into one part of your thyroid function. Therefore, it is not considered a full thyroid test on its own.

Free T3 (triiodothyronine) Test

One of the hormones that the thyroid produces is called T3 (triiodothyronine). Most of the T3 in the body is bonded to protein, however, the T3 that is not bonded and circulates freely is called free T3. The Free T3 Test measures the amount of nonbonded T3 in the body.

T3 tests are most often used to diagnose hyperthyroidism or the severity of hyperthyroidism. Individuals with elevated T3 levels might indicate issues such as:

  • Graves’ Disease
  • Hyperthyroidism 
  • Silent Thyroiditis
  • Thyrotoxic Periodic Paralysis
  • Toxic Nodular Goiter

High levels of T3 might also indicate high levels of protein in the blood. A Free T3 test is crucial to measure the amount of free T3 in the body; however, it does not provide information by itself and is only considered a part of a full thyroid test.  

Free T4 (thyroxine) Test

T4 (thyroxine) is the inactive version of T3. The primary duty of T4 is to transport T3 to the proper organs throughout the body. T4 must be converted to T3 before it can be used. A Free T4 Test measures the amount of unbonded T4 available in the body. 

Elevated levels of T4 may indicate: 

  • Thyroiditis 
  • Toxic Multinodular Goiter 
  • Too much iodine
  • Too much thyroid replacement medication

Low levels of T4 may indicate:

  • Hypothyroidism
  • Dietary issues (iodine deficiency, fasting, malnutrition)
  • Medications that affect protein levels
TPO Antibodies 

A TPO Antibodies Test measures the amount of Thyroid Peroxidase in the body. TPO (Thyroid Peoxidase) is an enzyme found in the thyroid gland that plays an important role in the production of thyroid hormones.

TPO essentially converts the iodine absorbed from our food to an active form of iodine that our body can use. Iodine is vital for the production of both T3 and T4. Elevated levels of TPO may indicate Hashimoto’s Thyroiditis. Hashimoto’s is an autoimmune disease where your immune system attacks your body’s healthy thyroid cells.  

It is vital to include TPO Antibodies in a full thyroid test as you could have high levels of TPO but still show normal TSH levels. Hashimoto’s Thyroiditis is the most common cause of hypothyroidism in the United States. With early detection, patients are more likely to be able to slow down the progression and better manage it. 

Reverse T3

Reverse T3 (rT3) is an inactive form of T3 and is the byproduct of T4. Though the importance of rT3 is widely debated, it can be an important marker in situations for patients that have undergone extreme trauma, stress, and/or surgery. Therefore, it is recommended as part of a full thyroid test. 

Tg (Thyroglobulin)

This test measures the level of thyroglobulin in your blood. Thyroglobulin is a protein that can be made by both normal and cancerous thyroid cells. Tg tests are most commonly used for cancer treatments to

  • See if the cancer treatment was successful 
  • See if cancer has returned after treatment 

If thyroglobulin levels stay the same or increase after treatment, it may mean there are still thyroid cancer cells in the body. If thyroglobulin levels decrease or disappear after treatment, it may mean there are no normal or cancerous thyroid cells left in the body.

Tg Antibody (TgAB)

This test measures the level of thyroid antibodies in the blood. This test is used to diagnose autoimmune disorders with the thyroid. 

Antibodies are proteins in the immune system that are meant to fight off foreign substances like viruses and bacteria. Sometimes antibodies will attack the body’s own healthy cells which can lead to an autoimmune disorder. 

What to expect and aftercare

The doctor's hand in the laboratory holds a test tube with blood

A blood draw is a procedure clinicians use to perform a full thyroid test. The technician at your health facility will draw your blood and send it to a laboratory for analysis and results. 

A blood draw is a routine procedure that is minimally invasive. During the following days after your blood draw, you may notice 

  • Slight bruising
  • Slight soreness

at the area where the needle was inserted. An over-the-counter-pain medication or ice pack will help ease the discomfort and should recede in a couple of days. 

If you experience any red or swollen discomfort or a large amount of pain, contact your doctor immediately as it could be a sign of infection. 

Key Takeaways

  • TSH alone is not able to provide a full picture of your thyroid health
  • A full thyroid test is suggested to include the following: TSH, T3 (triiodothyronine), T4 (thyroxine), TPO (Thyroid Peroxidase), Reverse T3 
  • Each test measures a different component that is vital to your thyroid function 
  • Together, these tests provide information for a holistic and comprehensive view of your thyroid health 

If you want to better manage your blood tests, medications, symptoms, moods, energy levels, and weight changes, download our ThyForLife app to get a head start! ThyForLife is an all-in-one thyroid solution right at your fingertips. 

Here at ThyForLife, we do our utmost to provide accurate information. If you require more detailed information regarding medical terms, please consult your thyroid doctor. 


At ThyForLife, we do our utmost to provide accurate information. For detailed medical information regarding diagnosis, treatment, and general practices please consult your healthcare professional. Always listen to the advice of your healthcare provider.
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