The importance of thyroid testing:

It’s not just for women

Published May 18, 2023. Last updated August 10, 2026

The thyroid gland is a small but powerful part of your endocrine system. Its main job is to produce certain hormones, which are released into your bloodstream and carried to every tissue in your body. These hormones help regulate your metabolism, or how well your body converts food into energy.¹

Because every cell in your body needs energy to function, thyroid hormones can affect everything your body does. They help regulate heart rate, blood pressure, breathing, digestion, body temperature, cholesterol levels, weight, mood, memory, and muscle function. They also help support fertility and keep skin, hair, nails, and bones healthy. In women, thyroid hormones help manage the menstrual cycle.²

Thyroid disorders can affect men and women of all ages. They can happen when the thyroid produces too much (hyperthyroidism) or too little (hypothyroidism) hormone. Testing is important, especially if thyroid conditions run in your family, since undiagnosed thyroid issues can increase the risk of obesity, infertility, sexual dysfunction, osteoporosis, and heart disease.²

Common thyroid conditions and disorders

Hypothyroidism

Hypothyroidism, or an underactive thyroid, is when your thyroid doesn’t make enough thyroid hormones. Because many bodily functions rely on these hormones, low levels can slow things down and lead to symptoms like fatigue, brain fog, forgetfulness, cold sensitivity, joint and muscle pain, constipation, hair loss, and weight gain.³

Men may also experience low testosterone, sexual dysfunction, or infertility. Women may experience heavy or irregular periods or infertility. In teens, it can slow growth and delay puberty. Although hypothyroidism can affect anyone, it’s especially common in women between ages 30 and 50 and in adults over age 60.⁴,⁵

Hashimoto’s thyroiditis is the most common cause of hypothyroidism in the US. Other causes include inflammation of the thyroid gland, certain medications, too much or too little iodine, goiter (an enlarged thyroid), and other conditions that affect thyroid function.²

Hyperthyroidism

Hyperthyroidism, or an overactive thyroid, is when your thyroid makes too much thyroid hormones. High levels can speed up many bodily functions and lead to symptoms like anxiety, irritability, heat sensitivity, muscle weakness, fatigue, and weight loss.³

Men may also experience thinning hair, low sex drive, sexual dysfunction, or infertility. Women may experience lighter or fewer periods or infertility. In teens, it can cause rapid growth, restlessness, hyperactivity, or difficulty concentrating. Hyperthyroidism can affect anyone, but it’s more common in adults over age 60.

Graves’ disease is the most common cause of hyperthyroidism in the US. Other causes include inflammation of the thyroid gland, certain medications, too much iodine, thyroid nodules (small lumps or growths), and, less commonly, thyroid cancer.²

Key markers of thyroid health

Every marker reveals a specific part of thyroid function: the signal that tells your thyroid what to do, the active hormones your body can use, and the immune activity that may interfere. Understanding what each test measures (and why) can help you better understand where your thyroid health stands.

Thyroid-stimulating hormone (TSH)

Your thyroid doesn't decide on its own how much hormone to make. It responds to TSH, a hormone made by the pituitary gland, which tells the thyroid to produce T3 and T4.

The pituitary constantly monitors thyroid hormone levels in your blood and adjusts TSH up or down to keep them in range. When thyroid hormone levels are low, TSH rises. When they’re high, TSH falls. But this response isn’t balanced: small changes in thyroid hormone levels can cause much larger swings in TSH. This makes TSH the more sensitive marker. It may flag changes in thyroid function before T3 and T4 levels move out of range.¹

Triiodothyronine (T3) and thyroxine (T4)

Your thyroid makes mostly T4, along with a smaller amount of T3. These hormones circulate in the bloodstream in 2 forms: bound and free. Most of T3 and T4 is bound to carrier proteins, and only a tiny fraction circulates freely.

• Bound T3 and bound T4 are attached to carrier proteins and can’t enter tissues
• Free T3 and free T4 are unattached and can enter tissues to do active work

Free T3 and T4 tests measure only the unbound portion of thyroid hormone in the blood. Total T3 and T4 tests measure both the bound and free hormones together. Since most thyroid hormone s are bound, total levels can shift due to pregnancy or other factors unrelated to thyroid function. Measuring free hormone levels can show the amount of thyroid hormone available for your body to use.¹

Thyroid peroxidase (TPO) antibodies and thyroglobulin (Tg) antibodies

Sometimes the immune system can mistake thyroid proteins for a threat and produce antibodies against them. TPO antibodies target thyroid peroxidase, an enzyme your thyroid uses to make T3 and T4. Tg antibodies target thyroglobulin, a protein your thyroid uses to build T3 and T4.

Testing for antibodies alongside hormone levels can help identify if thyroid changes may be related to autoimmune activity. Two of the most common autoimmune thyroid conditions are Hashimoto's thyroiditis and Graves' disease. In Hashimoto's, the immune system gradually damages the thyroid, making it harder to produce enough hormone over time. In Graves' disease, the immune system overstimulates the thyroid, causing it to produce too much.¹,³

Only about 50% of women under 45 with hypothyroidism are treated, and even fewer men are.

Nutrients impacted by thyroid disorders

Thyroid health and nutrition go hand in hand. Thyroid disorders can make it harder for your body to get the nutrients it needs. Your thyroid relies on 4 important nutrients to function properly: iodine, iron, selenium, and vitamin D. These nutrients help support and protect overall thyroid health.

When these nutrients are lacking, thyroid hormone production can be disrupted, making thyroid symptoms worse. But there’s a twist: thyroid disorders can also cause nutrient deficiencies. This relationship creates a cycle where thyroid disorders and nutrient deficiencies feed into—and potentially worsen—each other. Understanding this connection and correcting any nutrient deficiencies is essential for supporting thyroid health and overall well-being.

The Quest Thyroid TSH Function Test checks your levels of thyroid stimulating hormone (TSH)—produced in the pituitary gland—and can help confirm if your thyroid is working properly. Based on your hormone level, further testing may be required to help identify any thyroid disorders.

This test is also part of larger test panels on questhealth.com, such as:

• Comprehensive Thyroid Test Panel
• Basic Health Profile – Women's
• Comprehensive Health Profile – Women's
• Elite Health Profile
• Fatigue Test Panel
• Fitness Profile – Elite Test
• Post-COVID-19 Basic Test Panel
• Post-COVID-19 Expanded Test Panel
• Pre-Pregnancy Test Panel
• Menopause & Perimenopause Assessment Test Panel
• Post Menopause Assessment Test Panel
• Women's Hormone Test Panel – Basic
• Women's Hormone Test Panel – Extended

If you’ve already been diagnosed with a thyroid disorder, Quest offers 2 Thyroid Disorder Monitoring tests to measure key hormones in thyroid function while you’re undergoing treatment.