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Recommended Tests for Hypothyroidism Diagnosis

Learn what labs can help diagnose your hypothyroidism.
Recommended Tests for Hypothyroidism Diagnosis
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All our cells need the right amount of thyroid hormone to function. Too little or too much thyroid hormone can result in changes in how our body functions. For instance, too little thyroid hormone (hypothyroidism) causes your body to slow down. While we can feel the effects of hypothyroidism through our symptoms, how do we tell what is going on inside?

Through lab testing, your healthcare provider better understands what is happening in your body. In this article, we're looking at various tests that give an overall picture of your thyroid health and help in diagnosing hypothyroidism.

Overview of thyroid hormone regulation

Your thyroid gland releases thyroid hormones: thyroxine (T4) and triiodothyronine (T3). While the majority of thyroid hormone is in the form of T4, a small amount is T3. For thyroid hormone to affect our cells, it has to be in the form of T3. This conversion, T4 to T3, happens in specific cells in your body.

As more T4 converts to T3, your T4 level drops. Your pituitary gland, located in your brain, senses this. As a result, it produces a hormone called thyroid stimulating hormone (TSH). This hormone tells your thyroid gland to release thyroid hormone. Your pituitary gland will keep secreting TSH until the T4 level in your blood gets to a certain level. Once there, your pituitary gland stops TSH production.

This cycle repeats, helping to regulate thyroid hormone production. A change to any of these “major players” can ultimately affect the release of thyroid hormones.

Thyroid function tests

Now with a complete picture of thyroid hormone regulation, let’s take a closer look at tests used to determine the function of your thyroid.

Thyroid-stimulating hormone (TSH)

For the majority of people, an assessment of the TSH is a key thyroid function test, and one of the first lab values your healthcare provider looks at to determine your thyroid function.

As previously mentioned, TSH stimulates your thyroid gland to release thyroid hormone. Generally, a high TSH means your thyroid gland produces too little thyroid hormone (primary hypothyroidism). A low TSH means your thyroid gland produces too much thyroid hormone (hyperthyroidism). A healthy thyroid has a TSH level that falls in the normal range. 

You can have a low TSH in secondary hypothyroidism. This means your pituitary gland isn’t making enough TSH to stimulate your thyroid gland.

Free thyroxine (Free T4)

T4 and T3 travel throughout your body bound to transport proteins. When they are bound, they are unable to enter your cells. Only free T4 and T3 can enter your cells. As transport protein levels change in your body, bound T4 and T3 levels change as well. This makes bound T4 and T3 levels unreliable for determining thyroid function.

A Free T4 level more accurately shows how well your thyroid gland is functioning. When used in combination with a TSH level, you get a pretty accurate picture of how well your thyroid gland is functioning.

A high TSH with low Free T4 means your thyroid gland can’t produce enough thyroid hormone. This indicates primary hypothyroidism. A low TSH and low Free T4 indicate a problem with your pituitary gland as seen in secondary hypothyroidism.

Free Triiodothyronine (Free T3)

T3 is the active thyroid hormone, and while the conventional diagnosis of hypothyroidism looks primarily at the TSH and Free T4 level, the Free T3 level can help evaluate the degree of severity of hypothyroidism and symptomology. 

Thyroid antibody tests

Your immune system makes antibodies to help protect your body from bacteria or viruses. But sometimes your immune system makes antibodies against your healthy cells.

Hashimoto’s, an autoimmune disorder, occurs when your immune system develops antibodies against your thyroid cells. Because of this, the destruction of healthy thyroid cells affects thyroid hormone production.

When this occurs, thyroglobulin and thyroid peroxidase antibodies appear in your blood. In general, thyroid antibody levels don't tell us how your thyroid functions. But they do help determine the cause of your hypothyroidism.

Thyroid Imaging

Although not blood tests, imaging can also help determine your thyroid function.

  • Radioactive iodine uptake: Iodine is essential for making thyroid hormones. This test measures how much iodine your thyroid gland takes up.
  • Thyroid ultrasound: Hypothyroidism can change how your thyroid tissue looks on an ultrasound thyroid scan, and in some cases, cause nodules on the gland that can be detected via ultrasound. 

Other labs

Thyroid hormone levels like TSH, Free T4, and Free T3 give you the best picture of your thyroid function. But other labs might be useful to help with symptom management and optimizing your thyroid health.

  • Nutrient levels: Many nutrients, especially zinc and selenium, play a role in thyroid hormone production and maintaining the health of your thyroid. Knowing your levels allows you to identify and correct nutritional deficiencies.
  • Ferritin level: Iron helps in the conversion of T4 to T3 and the making of red blood cells. Without enough iron, you can develop a condition called iron-deficiency anemia. Over 40% of those with hypothyroidism have iron deficiency anemia. Measuring your ferritin levels allows you to see how much iron your body stores.
  • Gut microbiome makeup: Your gut microbiome plays a key role in nutrient absorption and creates a barrier, preventing toxins from entering your body. A 2018 study linked alterations in your gut microbiome to Hashimoto’s. The best way to test your gut microbiome is through stool sampling.
  • Sex hormones (estrogen and testosterone): A 2021 study showed an association between thyroid function, sex hormone levels, and sex hormone binding protein concentrations (SHBG). Through complex pathways, they all affect each other. Measuring SHBG and sex hormone levels may provide more information on how your thyroid functions.
  • Cortisol: Sometimes referred to as the “stress hormone,” your adrenal glands make cortisol in response to stress and other factors. A small 2016 study showed that those with Hashimoto’s had high cortisol levels. Yet, the exact link between cortisol and autoimmune disorders is still being debated. Cortisol levels are easy to measure through a blood, saliva, or urine sample.

A note from Paloma Health

Knowing your thyroid levels is the first step to making sure your thyroid is functioning correctly. Try Paloma's convenient, at-home testing kit. It measures TSH, Free T4, Free T3, and Thyroid Peroxidase Antibodies (TPOAb). You also have the option of adding on a Reverse T3 and/or Vitamin D test.

Never try to interpret your thyroid testing lab results yourself. Instead, work with a Paloma Health thyroid specialist to help you understand your results and create the best treatment plan for your underactive thyroid. Make an appointment for a virtual visit, to receive quality care from the comfort of your own home today.

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Emilie White, PharmD

Clinical Pharmacist and Medical Blogger

Emilie White, PharmD is a clinical pharmacist with over a decade of providing direct patient care to those hospitalized. She received her Doctor of Pharmacy degree from Massachusetts College of Pharmacy and Health Sciences. After graduation, Emilie completed a postgraduate pharmacy residency at Bon Secours Memorial Regional Medical Center in Virginia. Her background includes caring for critical care, internal medicine, and surgical patients.

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