What are thyroid hormones? The thyroid is a small gland that sits at the front of your neck. It’s responsible for controlling many of the body’s key activities – such as metabolism. It does this by releasing specific hormones into the bloodstream.

A hormone is small chemical messenger that allows different parts of your body to “talk” with each other. The thyroid makes two kinds of hormones: thyroxine (or T4) and triiodothyronine (or T3). These hormones circulate in your blood, allowing the thyroid gland to regulate many of the body’s important functions, such as:

Metabolism – Thyroid hormones tell the body when to burn fat, which gives you more energy. Thyroid hormones can also trigger the production of glucose – a sugar formed from carbohydrates – to provide your body with more energy.

Heart rate – Thyroid hormones can affect your resting heart rate (the number of times your heart beats in a minute when you’re at rest).

Internal body temperature – Thyroid hormones are involved in regulating your body’s internal temperature – so the thyroid gland acts a bit like a thermostat that helps make sure your body doesn’t get too cool or too hot.

What’s more, thyroid hormones can contribute to more wakefulness and alertness because of how they affect the nervous system.

In short, your body requires the right balance of thyroid hormone levels in order to effectively carry out many of its functions.

Thyroid-Stimulating Hormone (TSH)

While the thyroid gland helps regulate many processes in the body, another gland (the pituitary) is in charge of controlling the thyroid’s activity. The pituitary gland does this by releasing a hormone of its own – thyroid-stimulating hormone, or TSH – into the bloodstream, which carries TSH to the thyroid gland.

TSH tells the thyroid to pump out more thyroid hormones. So when your body needs more thyroid hormones, the pituitary gland will increase the amount of TSH in your blood. Thus, if a thyroid test shows you have a high level of TSH, this can mean that your thyroid is underactive: it’s not making enough hormones. It can also mean that more TSH is required to keep thyroid hormone levels normal, which may indicate an evolving problem with the thyroid gland itself.

What’s included in a full thyroid panel? A full thyroid panel usually checks thyroid-stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4) levels. In some cases, a blood test for thyroid function will also check your blood’s level of TPO antibodies. If you have abnormal thyroid hormone levels, high levels of TPO antibodies can point to an autoimmune thyroid disease as a possible reason for those abnormal levels.

How does a blood test for hypothyroidism work? How to test for hypothyroidism? It’s important to note that there is no hypothyroidism test that can check thyroid hormones and—based only on those test results—conclusively determine if someone has hypothyroidism. That’s because both thyroid hormone testing and a physician’s evaluation of symptoms and medical history is required for a diagnosis. A blood test for hypothyroidism is based on your levels of thyroid-stimulating hormone (TSH) and the thyroid hormones T3 and T4. Because TSH signals the thyroid gland to produce more thyroid hormones, unusually high levels of TSH can mean that your thyroid isn’t making enough hormones. A thyroid lab test might also measure T3 and T4 to reveal just how low your thyroid hormone levels are, which can help your healthcare provider decide on a treatment strategy.

How does a blood test for hyperthyroidism work?

A blood test for hyperthyroidism evaluates your levels of thyroid-stimulating hormone (TSH) and the thyroid hormones T3 and T4. Because TSH signals the thyroid gland to produce more thyroid hormones, unusually low levels of TSH can mean that your thyroid is making too many hormones. T3 and T4 measurements can also reveal just how high your thyroid hormone levels are, which can help your healthcare provider decide on a treatment strategy.

What are thyroid nodules?

Thyroid nodules are small bumps that can form inside the thyroid gland. Approximately 90% of thyroid nodules are non-cancerous; however, in some cases, these nodules may suggest the presence of thyroid cancer. Also, thyroid nodules can sometimes alter thyroid hormone levels, resulting in either hypothyroidism or hyperthyroidism.

Women are about 4 times more likely than men to have thyroid nodules. And older age, a history of thyroid radiation, and iron deficiency are all linked with a greater likelihood of having thyroid nodules.