Your thyroid gland is probably not something you think about much unless you start experiencing unexplained symptoms that may be connected to this gland’s performance.

This butterfly-shaped gland plays a role in a surprising number of bodily processes, including metabolism, weight control, body temperature regulation, mental health, cognitive function, sleep quality, skin and hair health, and more.

Hypothyroidism is the term for when your thyroid gland is underactive. The condition can cause a host of symptoms related to the processes mentioned above. So if you notice unusual symptoms, talking to a clinician is always a good idea. They can order tests to help check your thyroid’s functioning and create a treatment plan for you after evaluating and interpreting your thyroid test results.

In this article, we explore how to test for hypothyroidism, thyroid labs, and more.

What is hypothyroidism?

Hypothyroidism occurs when the thyroid gland is underactive. This means it does not produce enough thyroid hormones. Thyroid hormones are chemical messengers that support many bodily processes.

Types of hypothyroidism:

• Primary: This issue occurs with the thyroid gland directly. It does not produce enough thyroid hormones because of damage or disease. The most common cause is Hashimoto’s thyroiditis, an autoimmune condition in which the immune system attacks the thyroid.
• Central: In this rarer form of hypothyroidism, the issue occurs in the brain, with either the pituitary gland (secondary hypothyroidism) or the hypothalamus (tertiary hypothyroidism) failing to adequately stimulate the thyroid gland.

Hypothyroidism affects about 5% of people in the United States and is more common in people assigned female at birth than those assigned male.

What are the common signs of hypothyroidism that might lead to testing?

Testing is not usually part of routine preventive care. So you might only experience testing if you notice symptoms and flag them for a clinician.

“We don’t recommend universal screening because the symptoms are very nonspecific and can overlap with other conditions,” says Sonia Gibson, MD, a board-certified endocrinologist. “Additionally, universal screening has not been shown to be beneficial for asymptomatic patients.”

She adds, “Patients may be screened for hypothyroidism when they present with symptoms of persistent fatigue, cold intolerance, unexplained weight gain and fluid retention, dry skin, brittle hair and nails, loss of eyebrows, menstrual irregularity or cognitive symptoms like brain fog.”

The table below shows symptoms for hypothyroidism. Some tend to be symptoms that show up first (early), while others may not appear until untreated hypothyroidism has progressed (late). Treatment, once you’re diagnosed, helps alleviate symptoms.

Common symptoms of hypothyroidism:

Your provider might also test you if you have risk factors for hypothyroidism.

“Testing might also be recommended,” Dr. Gibson adds, “if patients have a very strong family history or abnormal thyroid findings during a physical exam, [such as] goiter or enlarged thyroid.”

You might be more at risk for hypothyroidism if: 

• You’re female
• You’re over 60
• You have a family history of thyroid disease
• You have a history of thyroid issues or have undergone thyroid procedures
• You have a history of radiation treatment to the neck or head
• You have autoimmune disease, such as lupus or type 1 diabetes
• You have genetic conditions linked to a higher risk of hypothyroidism, including Down syndrome or Turner syndrome
• You’ve recently been pregnant
• You take medications that up your risk, such as amiodarone, lithium, or some medications to treat viral infections, cancers, and autoimmune diseases

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How is hypothyroidism tested?

Hypothyroidism is usually first tested with thyroid blood tests, as listed below. Some people may also need imaging tests. However, your provider will likely opt for thyroid function tests first.

You may only need just one test to confirm thyroid status. The following is a list of tests in a full thyroid panel, however:

• Thyroid -stimulating hormone (THS)
• Free thyroxine (fT4)
• Free triiodothyronine (fT3)
• Thyroid peroxidase antibodies (TPoAb)
• Thyroglobulin antibodies (TgAb)
• Reverse T3 (rT3)

Now let’s explore these different types of thyroid tests and how they check for hypothyroidism.

TSH

The first step to evaluating your thyroid gland is a blood test to check your levels of thyroid stimulating hormone (THS), a hormone that your pituitary gland secretes, Dr. Gibson explains. 

Even though your pituitary gland produces this hormone, it affects the thyroid gland by regulating the production of fT4 and fT3. The TSH blood test is the most sensitive test for checking thyroid function.

fT4

If your TSH is elevated, then your provider will likely measure fT4 to determine if you have overt (severe deficiency) or subclinical (mild or trending toward deficiency) hypothyroidism.

• High TSH + low f24 = overt
• High TSH + normal T4 = subclinical

Additionally, if your clinician suspects secondary hypothyroidism (a problem with the pituitary gland rather than the thyroid gland itself), they will likely test your ft4 level. In secondary hypothyroidism, TSH might be normal or low and ft4 will likely be low.

“Therapy is recommended for overt hypothyroidism,” Dr. Gibson says. “We often treat subclinical hypothyroidism if the patient is symptomatic, has risk factors, or is trying to conceive.”

fT3

Although this test is part of a full thyroid panel, it’s not usually relevant to hypothyroidism, since when the condition is present, fT3 is typically normal. However, your provider may choose to test it for various reasons.

TPoAb and TgaB

After confirming primary hypothyroidism, your provider might order TPoAb. This helps confirm Hashimoto’s thyroiditis. Typically TPoAb is enough to confirm, but sometimes a TgaB test is also performed.

rT3

This test measures the inactive form of T3. But it isn’t routinely used for testing for hypothyroidism.

When additional thyroid tests are needed

The tests mentioned above help you and your clinician understand what’s going on with your thyroid hormones. However, sometimes additional testing is required to assess other thyroid conditions or structural issues.

For example, imaging tests, such as an ultrasound, may be needed if your clinician detects a nodule or lump on your thyroid gland after physically examining you. Imaging tests include an ultrasound, a thyroid scan, and a radioactive iodine uptake test.

Additional testing might be needed if you have:

• A lump or nodule on your thyroid
• An enlarged thyroid gland
• Unusual symptoms, such as difficulty swallowing, unexplained hoarseness, or neck pain
• A history of radiation

Do symptoms of life stage affect testing?

Your thyroid hormones don’t exist in a vacuum. All hormones in your body have a complex interplay with each other as chemical messengers. That’s why you and your clinician also have to consider what else might be going on, including your life stage or any underlying conditions.

Pregnancy and postpartum

Pregnancy places extra demand on your body, including on the thyroid gland. This is because thyroid hormones play a role in fetal brain development. “During pregnancy, the thyroid hormone requirements increase,” Dr. Gibson says. “Patients with overt or subclinical hypothyroidism should be treated according to the trimester-specific TSH targets to avoid adverse pregnancy outcomes and abnormal fetal development.”

The postpartum period matters too. “Some patients might experience a condition called postpartum thyroiditis,” Dr. Gibson explains. “In this scenario, there is an initial hyperthyroidism phase followed by hypothyroidism.”

She adds, “This condition is typically self-limited, meaning it can resolve spontaneously without treatment, but there are cases where patients may remain hypothyroid and benefit from thyroid hormone treatment. The symptoms can be labeled as postpartum fatigue or depression, so thyroid testing is crucial if the symptoms are not resolving or are getting worse. “

Fertility planning

If you are experiencing symptoms that leave you or your clinician suspicious of hypothyroidism while you are trying to conceive, testing can help confirm or rule out the condition. Treatment may be necessary ahead of pregnancy.

PCOS and overlapping symptoms

Polycystic ovary syndrome (PCOS) and hypothyroidism share some overlapping symptoms, such as fatigue, weight gain, high cholesterol levels, anxiety and depression, hair loss, and irregular menstrual cycles. Additionally, hypothyroidism is more common in people with PCOS. So your clinician may evaluate you for both conditions based on your unique set of symptoms.

Perimenopause and midlife shifts

“Hormonal shifts are common,” Dr. Gibson says, “and this is very relevant during menopause for example. Declining estrogen symptoms can overlap with symptoms of hypothyroidism.” Additionally, hypothyroidism is more common in people who are postmenopause, and menopause symptoms may be worse when hypothyroidism is present. For this reason, if thyroid testing may come up for you as you enter this midlife transition.

Other conditions

“Other conditions like anemia, stress, and lack of sleep can also overlap with hypothyroid symptoms,” Dr. Gibson says, “which is why it is so important to perform necessary testing rather than treating empirically, as symptoms alone can be unreliable.”

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How to prepare for a thyroid blood test

You might be wondering if thyroid testing requires special preparation. “Fasting is typically not necessary for thyroid testing,” Dr. Gibson says.

However, you may need to stop taking certain supplements about two to three days prior to testing. “Some supplements like high dose biotin, typically found in hair and nail products, can interfere with the thyroid lab testing, causing a false result,” she explains.

Your health status at the time of testing also matters. “Other situations where TSH might be temporarily altered include during an acute illness,” Dr. Gibson says. “So we don't typically recommend testing when patients are acutely ill, like with the flu or COVID, and wait until the patient is fully recovered to test for thyroid conditions.”

Key takeaways

• Having hypothyroidism means you have an underactive thyroid gland.
• Testing for hypothyroidism involves a simple blood test, though sometimes imaging tests may also be required.
• If you suspect you have hypothyroidism because of unexplained symptoms, Allara can help investigate and tailor a treatment plan to you.

FAQ

How do I check myself for hypothyroidism?

You can watch for thyroid symptoms to appear, but the only way to check for hypothyroidism, or other thyroid issues, is through a blood test analyzed by a clinician.

What are the warning signs of hypothyroidism?

Hypothyroidism can present with a host of symptoms, including weight gain, fatigue, hair and skin changes, cold intolerance, and more. These issues can also show up with other conditions, so if you have unexplained symptoms, talking to a clinician is a good idea. They can perform a simple blood test to check if you have hypothyroidism.

Is hypothyroidism dangerous? 

Yes, severe hypothyroidism can be dangerous if left untreated. But daily medications can help treat the condition and prevent complications.

Is hypothyroidism genetic?

Yes, hypothyroidism can be genetic. You are more at risk for hypothyroidism if your family has a history of the condition.

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