Thyroid Lab Tests 101

by | September 23, 2020 | Articles, Thyroid health

Though small in size, the thyroid plays a significant role in the functioning of the body. This butterfly-shaped endocrine gland is located in the front, lower portion of the neck and works to secrete hormones, like T4 or thyroxine. These hormones act throughout the body impacting areas of metabolism, development, growth, and even body temperature. In fact, during infancy, brain development is dependent upon adequate thyroid hormone.

Thyroid Conditions

Since this gland plays such a pivotal role in the body, it can have devastating effects when not working properly. Two commonly known conditions of the thyroid include hyperthyroidism, or an overproduction of thyroid hormones, or hypothyroidism, a low production of these hormones.

When experiencing hyperthyroidism, individuals may have nervousness, fatigue, irritability, muscle weakness, trouble sleeping, hand tremors, rapid and irregular heartbeats, difficulty tolerating heat, frequent bowel movements, weight loss, mood swings, and goiter, or swelling of the gland. In women, hyperthyroidism can cause infrequent periods, or absence of a period, if severe.

On the other hand, those with hypothyroidism may have fatigue, constipation, dry skin, goiter, voice hoarseness, sensitivity to cold, muscle weakness, aches, and tenderness, stiff joints, thinning hair, a slowed heart rate, depression, impaired memory, edema (swelling) and more. In women, hypothyroidism can cause heavy periods, infrequent periods, or loss of a period.


If experiencing these symptoms, it’s imperative to be tested to rule out these conditions. There are a variety of blood tests that are readily available to not only diagnose these, but to find the cause of them. These common blood tests include:

TSH Testing

This test looks at the Thyroid Stimulating Hormone (TSH) levels in your blood and is usually the best place to start when investigating the functioning of this gland. That is because changes in the TSH can actually alert a medical professional to abnormal hormone levels before symptoms occur. 

High levels of TSH show that this gland is not making enough hormones and hypothyroidism may be an issue. On the other hand, low levels of TSH usually indicate hyperthyroidism and an overproduction of thyroid hormones, which are downregulating TSH production. An exception to this is when low TSH indicates secondary hypothyroidism. In the case of secondary hypothyroidism, thyroid hormones are low, rather than high, as in hyperthyroidism.

Free and Total T4

As mentioned, T4 is the primary thyroid hormone secreted by the thyroid gland. With the total T4 blood test, the amount of bound and free hormones are measured and these can change when binding proteins differ. The Free T4 test looks at T4 that is not bound and able to readily enter tissues and convert to T3. This test is typically ordered when the TSH result is abnormal. Some healthcare practitioners routinely order thyroid hormone tests, to accompany TSH, to assess the overall thyroid function.

If there is an issue with this gland, these tests may show: 

  • Elevated TSH with low FT4 indicating disease causing hypothyroidism  
  • Low TSH with elevated TF4 showing hyperthyroidism
  • Low FT4 and low TSH indicating a problem upstream (e.g., the pituitary gland) causing hypothyroidism

Free and Total T3

If an individual has hyperthyroidism, their T3 hormone, or triiodothyronine, levels will be elevated, therefore, a total T3 test helps to determine if this condition is present and how severe it is. On the flip side, it’s not a great indicator of hypothyroidism as a patient can have high TSH and low FT4, while still having normal T3 levels. While measuring free T3 is possible, it’s not extremely reliable, and it is not done routinely. A low T3 can signify a severe illness, thyroiditis (inflammation of the thyroid gland), starvation, or an underactive thyroid gland.

Reverse T3

A reverse T3 (RT3) measures the inactive form of the T3 hormone. T4 converts to both T3 and RT3 in a specific ratio. When this ratio is off, it may be indicative of an issue with this endocrine gland. Stressors such as severe illness requiring critical care, or even caloric deprivation can also impact reverse T3 production. Currently, it is not recommended that reverse T3 be measured routinely. If it is measured, it must be taken into account with other thyroid function tests, including TSH, free T4 and total T3. 

TPO and TG Antibody Tests

When thyroid function tests show an underactive thyroid gland, measuring the levels of antibodies in this gland can help identify the cause of these problems. For example, positive anti-thyroid peroxidase (TPO) antibodies may show that an individual’s hypothyroidism could be the result of Hashimoto’s Thyroiditis.

On the other hand, the thyroglobulin (TG) antibody is a protein manufactured by normal thyroid cells and cancer cells. This test does not measure thyroid function, but instead is used for patients who have had surgery for thyroid cancer and need to have their levels monitored after treatment.

Get Help Today!

If you suspect your thyroid hasn’t been functioning correctly, it may be time to get help. Call our office to schedule your appointment with Dr. Bojana Jankovic Weatherly and get the support you need today. Dr. Bojana and her team are passionate about not only restoring health, but helping you find joy and fulfillment in life again!


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