Your thyroid is a crucial gland that manufactures vital hormones involved in various physiological systems, such as heart health, nervous system, reproductive function, bone growth, digestion, and other essential body functions.

How do you know when you’re suffering from one thyroid disease or the other? You will need to have thyroid blood tests to assess thyroid function. They measure levels of hormones such as TSH, free T3, free T4, total T3, total T4, and RT3 in your bloodstream.

Why are these tests necessary? According to research, approximately 20 million Americans suffer from thyroid disorders. Out of this number, about 60% are unaware that they have a thyroid disorder. Taking these tests is crucial because they provide vital information about your thyroid function, enabling prompt initiation of treatment if a disorder is detected. Early intervention can help manage symptoms effectively and improve overall health.

However, to get the best of your thyroid test results, you need to not only take the blood test correctly but also interpret them appropriately. That’s is why this article is so important. Here, we discuss each one of the necessary thyroid function tests and share a comprehensible guide on how you can understand your thyroid test results. Ready? Let’s move!

Blood Tests for Thyroid Function

Why You Should Ask for a Full Thyroid Panel

For a comprehensive understanding of your thyroid health, or if your TSH levels are normal but you’re still experiencing symptoms of hypothyroidism or hyperthyroidism, it’s essential to request a complete thyroid panel. It should include Free T4, Free T3, RT3, and antibody tests to rule out conditions like Hashimoto’s or Graves’ disease. Many doctors might only order 1-2 standard tests, but you should insist on having these additional tests. Consider ordering them out-of-pocket from companies or labs that offer these services if necessary.

TSH (Thyroid Stimulating Hormone) Test

The pituitary gland, situated at the base of the brain, produces TSH (thyroid-stimulating hormone). This hormone travels to the thyroid gland, directing it to produce the essential thyroid hormones—primarily T4 (thyroxine) and T3 (triiodothyronine). Elevated TSH levels typically indicate an underactive thyroid, while lower levels suggest an overactive gland.

Doctors often focus on TSH when evaluating thyroid function. Despite its usefulness, TSH alone may not be the best tool for detecting and treating thyroid disorders. Why is this? The main issue is that the TSH test alone doesn’t provide a complete picture of your thyroid health.   Research shows TSH can indicate how well your thyroid gland is working. Still, it doesn’t reveal other factors, such as thyroid status in peripheral tissues, thyroid hormone conversion, and thyroid hormone cellular activation.

Additionally, there’s the issue of suppressed TSH, which occurs when the body’s TSH level is lower than normal, while T4 and T3 levels remain within the normal range. TSH suppression can result from excessive thyroid medication or from treatments aimed at increasing T3 levels in patients with conversion issues that cannot be resolved with T4 alone. Other factors contributing to TSH suppression include the use of medications like glucocorticoids, dopamine agonists, somatostatin analogs, and rexinoids. Graves’ disease is also known to cause suppressed TSH levels.

T4 (Thyroxine) Test

A T4 test measures the amount of the T4 hormone in your blood. Doctors typically test for T4 alongside TSH. Thyroxine is one of the two main hormones that the thyroid gland produces. And it is known to increase numerous enzymes that produce energy for the body. The T4 test is instrumental in evaluating thyroid function and diagnosing thyroid disease.

Here’s one thing to keep in mind: T4 isn’t as biologically active as T3. This means it has different biological effects than T3 and does not activate your cells in the same way. This raises the question: what purpose does T4 serve?

The answer is simple. T4 levels are crucial for normal thyroid function because the body needs T4 to produce T3. Additionally, T4 has some cellular activity; it’s just not as potent as T3.

There are two types of T4 hormone tests:

• This test measures the form of T4 that is unbound and active, capable of entering your body tissues where needed. It is often preferred over a total T4 test because free T4 represents the portion of T4 that your body can utilize.
• Total T4 test:  This test measures both free T4 and bound T4. Bound T4 is attached to proteins and cannot enter bodily tissues. Interestingly, about 99% of T4 in your body is in this bound form. While a free T4 test provides valuable information about thyroid function and health, a total T4 test that includes both free and bound T4 is also beneficial.

T3 (Triiodothyronine) Test

Did you know that T3 is your body’s most potent thyroid hormone? When stimulated by TSH, your thyroid gland directly synthesizes T3. But why is this hormone so important? Well, T3 affects virtually every cell in your body. Considering its higher activity compared to T4 and its essential role in bodily functions, it becomes clear why doctors should include T3 hormone testing in thyroid lab panels.

Research indicates that various conditions can disrupt thyroid function, often without being detected by routine TSH testing alone, highlighting the importance of measuring free T3 levels.

Similar to T4, T3 tests are available in free T3 and total T3 tests. Here’s how they break down:

Free T3

This is the quantity of active thyroid hormone that isn’t bound. The amount of free T3 in your blood provides you a sense of how active your thyroid is at the cellular level.

However, you can only measure the amount of free and active thyroid hormone available to your body by measuring free T3. This hormone is in charge of adhering to the surface and nucleus of your cells and causing genetic alterations in those cells.

It is, therefore, reasonable to claim that a free T3 test is one of the most useful (if not the most useful) tools for determining T3 availability in your system and the state of your thyroid health, especially in the short term.

Total T3

This test determines the total quantity of T3 in the bloodstream. In other words, it measures the FT3 and the bound T3. Bound T3 is T3 fused to protein and therefore not available to be used by the body.

RT3 (Reverse Triiodothyronine) Test

The Reverse T3 (RT3) test measures the inactive form of the hormone T3, or triiodothyronine, in the body. Your body can convert T4 into either reverse T3 or T3. Let’s explain this better: When T4 converts to reverse T3, a particular thyroid hormone molecule cannot be activated into T3. But that’s not all; while RT3 has little biological activity and is considered an inactive compound, the belief that RT3 tests have limited clinical use is only partially accurate. There are situations where these tests can provide valuable insights into thyroid function.

A study shows that T3 and reverse T3 often compete for cellular binding. By converting T4 to reverse T3, your body lowers your circulating T3 levels, making it harder for the remaining T3 to bind to and activate your cells.

Holistic health practitioners consider reverse T3 an anti-thyroid metabolite. By “anti-thyroid metabolite,” we mean that RT3 is the hormone your body uses to slow down thyroid activity. But why does your thyroid need to produce fewer hormones during this time?

When you’re severely ill, your body can’t afford to burn energy as it usually does when you’re healthy. Therefore, your body reduces FT4 and FT3 and produces RT3 to slow your metabolism, allowing your immune system to conserve energy and help you heal faster.

The issue is that your body doesn’t only produce RT3 when you’re ill. Other factors like dieting, inflammation, nutrient deficiency, stress, intestinal dysfunction, and lack of sleep can also trigger its production.

These problems can cause weight gain, lower metabolism, fatigue, muscle pain, anxiety, and depression. Notice anything? These symptoms are very similar to hypothyroidism.

Well, that’s why your level of RT3 should never be taken lightly. Even if your T3 levels are within normal limits, if you have too much reverse T3 in your body, it can cause hypothyroidism symptoms. In such circumstances, naturopathic doctors emphasize the importance of examining reverse T3 and T3 to understand their interplay.

It’s critical to figure out why reverse T3 levels are higher than free T3 levels because identifying the underlying reasons is essential to addressing this issue. Licensed naturopathic doctors (NDs) emphasize treating the root causes. Addressing factors such as stress, inflammation, insulin resistance, overload of toxins and heavy metals, or nutritional deficiencies can help regulate thyroid hormone metabolism and, ideally, enhance the conversion of T4 to T3, the more active form.

T1 and T2

Thyroid hormone production involves T1 and T2, which were traditionally viewed as hormone precursors and by-products without direct biological activity. These hormones are not usually tested in clinical settings and do not directly bind to thyroid hormone receptors. Recent research has uncovered that T2 plays important roles by assisting T4 and T3 thyroid hormones in regulating the body’s metabolic rate and activating detoxification enzymes in the liver.

TSI (Thyroid Stimulating Immunoglobulins) Test

Thyroid-stimulating antibodies (TSIs) are antibodies that erroneously instigate the thyroid gland to become more active and release more thyroid hormone than your body needs into the bloodstream. As such, a TSI test is done to measure the level of thyroid-stimulating immunoglobulin in your blood.

If you have hyperthyroidism symptoms and your doctor suspects you have Graves’ disease, they will usually conduct a TSI test. If your TSH, T3, or T4 levels are abnormal, then conducting this test can help your doctor figure out what’s causing your symptoms.

Thyroid Antibodies (TgAb) Test

The thyroid antibodies test measures the level of thyroid antibodies in your blood. These antibodies, produced by the immune system, usually defend against invaders like viruses and bacteria. However, they can mistakenly attack the body’s cells, including healthy thyroid tissue. This autoimmune response can lead to thyroid diseases that, if untreated, may cause significant health problems. Research indicates that elevated TgAb levels are found in 20-40% of patients with Graves’ disease.
Thyroid antibodies can take different forms: some destroy thyroid tissue, and others stimulate excessive thyroid hormone production. Research shows that TgAb levels are elevated in 20-40% of patients with Graves’ disease.

Thyroid antibodies can take different forms: some destroy thyroid tissue, others stimulate excessive thyroid hormone production.

Thyroid Peroxidase Antibodies (TPO)

Thyroid peroxidase (TPO) is a naturally occurring thyroid gland enzyme essential for thyroid hormone synthesis. A TPO test measures the amount of antibody working against this vital enzyme.

Thyroglobulin Antibodies (Tg)

Thyroglobulin Antibodies This antibody  target thyroglobulin, the storage form of thyroid hormone. This test helps diagnose and monitor thyroid cancer.

Thyroid-stimulating Hormone (TSH) Receptor

This receptor normally binds to TSH. In Graves’ disease, however, two types of autoantibodies can bind to the TSH receptor, mimicking the action of TSH and leading to hyperthyroidism.

Thyroid Binding Inhibitory Immunoglobulin (TBII)

Thyroid Binding Inhibitory Immunoglobulin (TBII) can prevent Thyroid Stimulating Hormone (TSH) from attaching to its receptors, which disrupts the normal regulation of thyroid hormone production and can lead to hyperthyroidism. TBII is detected in the serum of patients diagnosed with Graves’ disease

Thyroid Binding Proteins Test (TBG)

Thyroid-binding globulin (TBG), also known as thyroid-binding protein, is produced by the liver and binds to T4 and T3 hormones, transporting them through the bloodstream. This allows them to regulate metabolism and perform other vital functions.

The serum TBG level test, also known as the thyroxine-binding globulin test, measures the amount of TBG in the blood. This test is valuable for identifying conditions that affect thyroid hormone levels. TBG levels may not significantly impact hypothyroidism or hyperthyroidism resulting from thyroid gland dysfunction.

When TBG levels are elevated, more thyroid hormone binds to TBG, reducing the amount of free thyroid hormone in circulation. This prompts increased thyroid-stimulating hormone (TSH) production, boosting thyroid hormone synthesis. Even without hyperthyroid symptoms, total thyroid hormone levels can rise.