Medically reviewed on August 17, 2022 by Jordan Stachel, M.S., RDN, CPT. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.
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Your thyroid gland fulfills several essential roles within your body. It produces hormones that affect your metabolism and aid with growth and development. When it’s working as intended, you won’t even know it’s there.
However, sometimes the thyroid kicks into overdrive, creating too many of these vital hormones. This increase in thyroid hormone production is known as hyperthyroidism—and it can lead to various health problems.
If you suspect you might have the thyroid disorder of hyperthyroidism, you’re not alone. An estimated 1% of Americans aged 12 and up are affected by an overactive thyroid gland. 
Are you wondering how to diagnose hyperthyroidism and what to do about having an overactive thyroid gland? We’ll be walking you through the process of assessing your thyroid nodule—from noticing the first signs and symptoms to testing for the condition.
Hyperthyroidism (not to be confused with hypothyroidism) occurs when your thyroid gland produces more hormones than necessary.
If you want to understand hyperthyroidism—which is also called overactive thyroid—it’s important to grasp how the thyroid nodule works. The butterfly-shaped thyroid gland sits at the front of your neck and generates two hormones:
These hormones are an essential part of your body’s normal functions. Among other things, T3 and T4 play a role in regulating digestion and metabolic rate. Essentially, they communicate with your cells, telling them how much energy to use.
Under typical circumstances, your thyroid gland sends out the right amount of hormones, producing new ones as the old ones do their job. However, when hyperthyroidism causes you to have too much T3 and T4, your body burns through energy quicker than usual.  The faster you use up your energy, the more tired, anxious, and run down you’ll feel.
Over time, you may also be at higher risk of more severe issues like: 
Although hyperthyroidism can be a serious affliction if left untreated, most people who treat it appropriately live long, healthy lives without issue.
Hyperthyroidism can arise due to thyroid conditions like:
Additionally, excessive iodine consumption can lead to an overactive thyroid. Your thyroid turns the mineral iodine into the hormones T3 and T4.  When you ingest too much iodine, your thyroid may produce excess hormones. You can consume too much iodine if you take medications containing the mineral (such as cough syrup or amiodarone). More rarely, a diet full of iodine-rich foods like kelp and seaweed can be the culprit.
Hyperthyroidism is more likely to affect people over 60, especially females.  People who smoke, suffer from diabetes, or have a family history of thyroid disease are also prone to hyperthyroidism. With that said, anyone can develop an overactive thyroid throughout their lives.
Curious about when to worry about your thyroid nodules? Because several issues can cause an overactive thyroid, the list of symptoms is long. Typical signs of hyperthyroidism include:
It’s worth noting that many of these issues are also symptoms of other conditions. If you notice one or two of these signs, don’t panic—you don’t necessarily have an overactive thyroid on your hands. The only way to know for sure is to test for hyperthyroidism.
Want to know how to diagnose hyperthyroidism? It’s a little complicated because many symptoms of an overactive thyroid are either invisible or typical of other diseases, it’s impossible to diagnose hyperthyroidism without testing.
Luckily, there are reliable ways to test for thyroid diseases like hyperthyroidism. Here are five of the most common methods you’ll come across.
The most widespread way to assess thyroid hormone levels is through a thyroid function test. Because the relevant hormones are present in your bloodstream, the thyroid blood test can can either be taken at home or with a healthcare provider.
The thyroid function test (also called a thyroid panel) measures the level of three hormones:
Some thyroid tests also test for thyroid peroxidase (TPO) antibodies. These antibodies bind to thyroid enzymes and suppress thyroid function. An elevated level of TPO antibodies can indicate an autoimmune disorder that causes hyperthyroidism.
By measuring thyroid hormone levels and antibodies, the thyroid function test can paint a picture of your overall thyroid health. If your test results come back with elevated levels of T4 or low TSH, you may have an overactive thyroid.  In that case, you’ll likely need to go through more blood tests to confirm.
Note: If you’re taking the B vitamin supplement biotin, your blood test may come back with false results.  For the most accurate thyroid blood test results, refrain from taking biotin 12 or more hours before your test. If you’re undergoing testing at a clinic, be sure to inform your healthcare provider that you take biotin.
Healthcare providers can also check for hyperthyroidism during a routine physical. Some of the external symptoms of an overactive thyroid are detectable during a checkup, including: 
Additionally, because unusual weight loss is a common symptom of hyperthyroidism, your healthcare provider may calculate your body mass index (BMI). By cross-referencing this measurement with the results of previous medical exams, you’ll be able to tell if you’ve lost weight.
When a blood test or physical examination indicates the possibility of hyperthyroidism, healthcare providers will typically order more tests. One such test is a thyroid scan.
Thyroid scans are a form of nuclear medicine, which involves injecting or consuming small amounts of radioactive material (called tracers) that special machines can detect.
A thyroid scan can see how iodine accumulates in your thyroid gland. As you’ll remember, iodine is a required component of usual thyroid function, but too much of it can cause problems.
Here’s how a thyroid scan works:
Your healthcare provider can then examine the images to determine the shape, size, and position of your thyroid gland. An enlarged or abnormally-shaped gland may mean that your thyroid is overactive.
Like the thyroid scan, a radioiodine uptake (RAIU) test relies on nuclear medicine. In this test, you’ll swallow a small dose of radioactive iodine several hours before your appointment.
However, with an RAIU test, technicians don’t take photos of your thyroid. Instead, they use a scanner that detects the amount of radiation given off by the radioactive tracer. Scans are taken four, six, or 24 hours after you ingest the tracer to see how your thyroid handles iodine. Sometimes, you’ll be scanned more than once.
Healthcare providers often order RAIU tests and thyroid scans together, as they involve similar processes.
Another possibility is a thyroid ultrasound. You may be familiar with ultrasound technology if you’ve ever been pregnant.
Ultrasound imaging—also called sonography—employs high-frequency sound waves to generate an image of your internal organs. In the case of a thyroid ultrasound, a technician will use a small probe known as a transducer to transmit sound waves into your body. These waves bounce off your thyroid to create a two-dimensional image of the gland.
Your healthcare provider can then use this image to check for:
Thyroid ultrasounds provide a similar image to thyroid scans. However, some patients prefer ultrasounds, as there is no radiation involved. With that said, thyroid ultrasounds give no insight into the actual function of the thyroid gland.
Ultimately, hyperthyroidism can cause a range of unpleasant symptoms, but it’s treatable—especially when you catch it early. In many cases, the first step in diagnosing an overactive thyroid is a blood test.
While you can always go to a clinic for a blood test, you could also learn how to check your thyroid at home. With an at-home Thyroid Test from Everlywell, you can assess your thyroid health as soon as you notice signs of an overactive thyroid—without going into a busy clinic.
Our quick and easy thyroid test measures your levels of free T3, free T4, TSH, and thyroid peroxidase antibodies (TPO). With accurate results available in a few days, you’ll confidently know which steps to take next to stay on top of your thyroid health.