How Hyperthyroidism Is Diagnosed

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If you have signs or symptoms of hyperthyroidism, it's important that you undergo a comprehensive evaluation so you can be properly and promptly treated, if necessary. Your doctor will do a thorough physical examination, review your medical history, and run detailed blood tests (such as TSH, T3, T4) to come to a diagnosis; imaging tests, such as thyroid ultrasound or CT scan may also be ordered. Hyperthyroidism can be managed but can cause complications if left untreated, so an early diagnosis is always best.

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Examination

After reviewing your symptoms and risk factors for thyroid disease, if your doctor suspects a potential diagnosis of hyperthyroidism, he will perform an in-depth examination focusing on your thyroid, but also other parts of your body.

Thyroid Examination

During the thyroid examination, your doctor will touch (palpate) your neck, looking for thyroid enlargement and nodules.

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

The presence of a thyroid thrill and/or bruit is highly suggestive of Graves' disease.

Physical Examination

Besides a thyroid examination, your doctor will examine the rest of your body for signs of an overactive thyroid.

For example, he will test your reflexes, as fast or hyper-responsive reflexes can be a sign of hyperthyroidism. He will also check your heart rate, rhythm, and blood pressure. This is because palpitations, atrial fibrillation, a racing heartbeat, or high blood pressure can be suggestive of hyperthyroidism as well.

Other parts of the physical examination include:

  • Examination of your skin, since unusually smooth and warm skin, may be a sign of hyperthyroidism. A small percentage of people with Graves' disease also develop a rash on their shins (pretibial myxedema).
  • Observation of the general quantity and quality of your hair, as thinning, fine, or shedding hair may signal a thyroid condition
  • Observation for any tremors, shakiness in the hands, or hyperkinetic movements such as table drumming, tapping feet, or jerky movements (often more severe in children)
  • Examination of your eyes, as red, bulging, dry, swollen, puffy, and watery eyes can be signs of a thyroid problem. In addition, "lid lag" (when the upper eyelid doesn't smoothly follow downward movements of the eyes when you look down) can be seen in hyperthyroidism.

Labs and Tests

Blood tests include a thyroid stimulating hormone (TSH) test, along with thyroxine (T4) and triiodothyronine (T3) tests. Your doctor may also test for thyroid antibody levels to confirm the diagnosis of Graves' disease.

It's important to review your test results with your doctor. Do not be afraid to ask questions. This is your health, so it's important you understand what is going on.

TSH Results

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 doctor will also check your T4 and T3 levels.

High Free T4 and T3 Results

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

As an aside, if your TSH is normal or elevated, and your free T4 and T3 are high, you will need an MRI of your pituitary gland to evaluate for a condition called central or TSH-induced hyperthyroidism.

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 still 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 possibility. 

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). 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 T4 levels are normal, you may have subclinical hyperthyroidism. This can also be seen in pregnancy.

Antibody Results

Testing your blood for antibodies, such as thyroid-stimulating immunoglobulin or TSH receptor autoantibodies, is important. 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 many cases, imaging tests, such as an ultrasound, radioactive iodine uptake (RAI-U), CT scan, or MRI will be performed to make a thorough and accurate diagnosis. 

Radioactive Iodine Scan

In a radioactive iodine uptake (RAI-U) 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 RAI-U results (the overactive gland usually takes up higher amounts of iodine than normal, and that uptake is visible in the X-ray).

In Graves' disease, RAI-U is high and you can see 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. In women who are pregnant or breastfeeding, a thyroid ultrasound is often used as an alternative to a radioactive iodine scan.  

CT Scan

A CT scan, known as computed tomography or cat scan, is a specialized type of X-ray that may help detect goiter, as well as larger thyroid nodules. 

Magnetic Resonance Imaging (MRI)

Like a CT scan or ultrasound, an MRI cannot tell a doctor 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, which contains iodine and can interfere with a radioactive iodine scan. 

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 (for example, 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 symptom that is more common in older people with hyperthyroidism.

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, as there are often several possible diagnoses. The good news is that a doctor can generally confirm or discount a diagnosis of hyperthyroidism easily and quickly with a medical history, physical examination, and some blood tests.

Finally, if your doctor diagnoses you with hyperthyroidism, he will then 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. 

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