How Hyperthyroidism Is Diagnosed

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If you have signs or symptoms of hyperthyroidism, it's important that you have a medical evaluation so you can start treatment. Your healthcare provider will do a physical examination, review your medical history, and run detailed blood tests to come to a diagnosis; imaging tests, such as a thyroid ultrasound, CT scan, or thyroid uptake scan may also be needed. Hyperthyroidism can be managed, but it can cause complications if it's not adequately treated, so an early diagnosis is best.

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Examination

After your provider reviews your symptoms and risk factors for thyroid disease, you will likely have a comprehensive physical examination, which can detect a variety of signs of thyroid disease.

Thyroid Examination

During the thyroid gland examination, your healthcare provider will touch (palpate) your neck, feeling for thyroid enlargement and nodules.

They will also palpate for what's known as a "thrill," which describes increased blood flow in the thyroid gland that can be felt. Your healthcare provider will also listen for a "bruit" with a stethoscope, which is the sound of increased blood flow to the thyroid gland.

The presence of a thyroid thrill or bruit is highly suggestive of Graves' disease, a common type of hyperthyroidism.

Physical Examination

In addition to a thyroid gland examination, your healthcare provider will examine the rest of your body for signs of an overactive thyroid.

For example, the healthcare provider will test your reflexes, since fast or hyper-responsive reflexes can be a sign of hyperthyroidism. They also check your heart rate, rhythm, and blood pressure. Palpitations, atrial fibrillation, a racing heartbeat, or high blood pressure can be suggestive of hyperthyroidism.

Physical examination signs of hyperthyroidism

  • Unusually smooth and warm skin can be a sign of hyperthyroidism.
  • A small percentage of people with Graves' disease develop pretibial myxedema, which is hardened areas of skin on their legs.
  • Thinning, fine, or shedding hair may signal a thyroid condition.
  • Tremors, shakiness in the hands, or excess movements such as table drumming, tapping feet, or jerky movements (often more severe in children) are common symptoms of high thyroid hormone levels.
  • Thyroid eye disease causes red, bulging, dry, swollen, puffy, and watery eyes, and "lid lag" (when the upper eyelid doesn't smoothly follow downward movements of the eyes when you look down).

Labs and Tests

Blood tests include a thyroid-stimulating hormone (TSH) test, and thyroid hormones—free thyroxine (free T4) and triiodothyronine (T3). Your healthcare provider may also test for thyroid antibodies, which is a sign that the body's immune system is attacking the thyroid gland.

Thyroid test results can be confusing so it's important to review your test results with your healthcare provider so you can understand your diagnosis.

TSH Results

TSH is released by the pituitary gland. It stimulates the thyroid gland to make thyroid hormones. When thyroid hormones are too high, as in primary hyperthyroidism (when the thyroid gland makes too much thyroid hormone), the pituitary gland will release less TSH.

The normal range for the TSH test is approximately 0.5 to 5.0 milli-international units per liter (mIU/L). All people with primary hyperthyroidism have a low TSH; however, the TSH level alone cannot determine the degree of hyperthyroidism. This is why your healthcare provider will also check your free T4 and T3 levels.

Different patterns of TSH, T3, and free T4 levels can be indicative of various stages or types of hyperthyroidism. For example, early Grave's disease can cause high T3 and high free T4, even with a normal TSH.

Thyroid disease treatment can also affect the blood test results.

Common conditions and the associated thyroid blood test results
 Lab results Condition
High TSH, high T3, high free T4 TSH-induced hyperthyroidism
Normal TSH, high T3, high free T4 Early Graves' disease
Low TSH, high T3, high free T4 Primary hyperthyroidism, including Graves' disease
Low TSH, high T3, normal free T4 Graves' disease, Thyroid nodules, Taking too much T3, Taking too much T4
Low TSH, normal T3, high free T4 Taking too much T4
Low TSH, normal T3, normal free T4 Subclinical hyperthyroidism, Early pregnancy
Any of these patterns can occur if the collection of the blood was taken at the wrong time.

High Free T4 and T3 Results

A low TSH, and a high free T4 and/or T3 blood test is consistent with a diagnosis of primary hyperthyroidism.

If your TSH is normal or elevated, and your free T4 and T3 are high, you might need an MRI of your pituitary gland to evaluate for a condition called central or TSH-induced hyperthyroidism. This is a rare condition that occurs when the pituitary gland makes too much TSH.

High T3 and Normal Free T4 Results

If your TSH is low and your T3 is high, but your free T4 is normal, it's likely that your diagnosis is Graves' disease or a thyroid nodule that is producing too much hormone. An imaging test called a radioactive iodine uptake scan can differentiate between these two diagnoses.

Taking too much T3 (called exogenous T3 ingestion) is another possible cause. 

Normal T3 and High Free T4 Results

If your TSH is low, your free T4 is high, but your T3 is normal, you may be experiencing hyperthyroidism from taking too much exogenous T4 (levothyroxine). Too much T4 also causes elevated T3 since T4 is converted into T3. Another possible diagnosis is an amiodarone-induced thyroid problem.

This lab combination may also be seen in people with hyperthyroidism who have a concurrent non-thyroidal disease (for example, a severe infection) that is decreasing the conversion of T4 to T3.

Normal Free T4 and T3 Results

If your TSH is low, but your T3 and free T4 levels are normal, you may have subclinical hyperthyroidism.

This can also occur during pregnancy. Total T4 is always elevated with the pregnancy hormones. TSH is usually suppressed in the first trimester by the action of pregnancy hormones on the pituitary gland.

Antibody Results

Testing your blood for antibodies, such as thyroid-stimulating immunoglobulin or TSH receptor autoantibodies, can help in the diagnosis of certain thyroid conditions.

A positive test confirms the diagnosis of Graves' disease, though some people with the disease do have a negative antibody test. In this case, a radioactive iodine uptake test (RAIU) can confirm the diagnosis. 

Imaging

In some cases, imaging tests, such as an ultrasound, radioactive iodine scan (RAIU), CT scan, or MRI, will be performed. 

Radioactive Iodine Scan

In a RAIU test, a small dose of radioactive iodine 123 is administered in pill or liquid form. 

Several hours later, the amount of iodine in your system is measured, accompanied by an X-ray. An overactive thyroid will often have elevated RAIU results (the overactive gland usually takes up higher amounts of iodine than normal, and that uptake is visible in the X-ray).

Possible results:

  • In Graves' disease, RAIU is high, and the test will show that there is uptake throughout the entire gland.
  • If you are hyperthyroid due to a nodule overproducing thyroid hormone, the uptake will be seen in that localized nodule. 
  • If you have thyroiditis as the cause of your overactive thyroid gland, the uptake will be low throughout the gland.

While radioactive iodine 123 is not harmful to your thyroid gland, it should not be given to women who are pregnant or breastfeeding.

Thyroid Ultrasound

A thyroid ultrasound can identify goiter, as well as nodules that may be causing hyperthyroidism. For women who are pregnant or breastfeeding, thyroid ultrasound is often used as an alternative to a radioactive iodine scan.

Computed Tomography (CT) Scan

A CT scan, also known as a CAT scan, is a specialized type of X-ray that may help detect goiter. CT contrast should be completely avoided in Grave's disease since large doses of iodine (such as in CT IV contrast) can severely exacerbate Graves's Disease.

Magnetic Resonance Imaging (MRI)

Like a CT scan or ultrasound, an MRI cannot tell a healthcare provider how the thyroid is functioning, but it can help detect goiter and thyroid nodules.

MRI is sometimes preferable to a CT scan because it doesn't require any injection of contrast. However, MRI is not useful in Grave's disease or hyperthyroidism.

Differential Diagnoses

While the symptoms of hyperthyroidism can be mistaken for heightened nervousness or stress, they can also mimic those of other common medical conditions.

For instance, unexplained weight loss could be a sign of a whole-body illness (such as an infection, non-thyroid autoimmune disease, or cancer). It could also be the first sign of a psychiatric illness, like depression or dementia, especially if a person is experiencing mood swings, irritability, or apathy.

A fast heart rate or irregular heart rhythm could be the first sign of a primary heart or lung problem or of anemia.

These examples are just the tip of the iceberg. The good news is that a healthcare provider can generally confirm or exclude a diagnosis of hyperthyroidism easily and quickly with a medical history, physical examination, and blood tests.

Finally, if your healthcare provider diagnoses you with hyperthyroidism, they will want to determine the cause of your hyperthyroidism (for example, Graves' disease versus thyroiditis). This can be sorted out with more blood tests and an imaging test called a radioactive iodine uptake scan. 

Frequently Asked Questions

  • What does a low TSH level mean?

    Low TSH usually means the thyroid is making too much thyroid hormone. It’s a sign that you may have hyperthyroidism, which can cause metabolic problems, high blood pressure, hair loss, dry skin, and other symptoms. Your healthcare provider will order additional tests to confirm the diagnosis.

  • When should you be treated for hyperthyroidism?

    Hyperthyroidism should always be treated. The American Thyroid Association recommends treatment for hyperthyroidism based on TSH levels and certain demographic characteristics:

  • If I have mild hyperthyroidism do I need medication?

    Mild hypothyroidism is defined as subclinical hypothyroidism, and it should be treated in certain circumstances.

    Treatment is recommended for TSH levels of 0.1 to 0.4 mIU per L for:

    • Age 65 and older
    • Postmenopausal women younger than 65 who are asymptomatic and not receiving estrogen or bisphosphonate therapy
    • Younger than 65 years who have heart disease, osteoporosis, or symptoms of hyperthyroidism 

    Treatment of TSH levels less than 0.1 mIU per L is recommended for:

    • Younger than 65 years
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8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Pirahanchi Y, Jialal I. Physiology, Thyroid Stimulating Hormone (TSH). In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing.

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  4. American Thyroid Association. Graves' Disease FAQ


  5. American Thyroid Association. Radioactive Iodine.

  6. Ross DS, Burch HB, Cooper DS, et al. 2016 American Thyroid Association Guidelines for Diagnosis and Management of Hyperthyroidism and Other Causes of Thyrotoxicosis. Thyroid. 2016;26(10):1343-1421. doi:10.1089/thy.2016.0229

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Additional Reading
  • Braverman, L, Cooper D. Werner & Ingbar's The Thyroid, 10th Edition. WLL/Wolters Kluwer.

  • Ross DS. Diagnosis of hyperthyroidism. Cooper DS, ed. UpToDate. Waltham, MA: UpToDate Inc.