Your doctor may suspect that you have Graves’ disease simply based on your medical and family history, combined with your symptoms. The next step—to make an accurate diagnosis—involves testing your thyroid to discover if it functions as it should, or if you have hyperthyroidism or hypothyroidism.
Before you have these tests, you should tell your doctor about all medications and supplements you take, since certain drugs (such as birth control pills and aspirin) can actually influence thyroid test results.
Graves’ Disease Blood Tests
Your doctor or endocrinologist will draw your blood in order to test certain hormone levels. He or she may want to measure the thyroid-stimulating hormone (TSH), T3 (triiodothyronine), and T4 (thyroxine) hormone levels. T3 and T4 are the major hormones produced by your thyroid. TSH, which is released by the pituitary gland, tells your thyroid to produce T3 and T4.
If your doctor can’t definitively diagnose Graves’ disease after looking at your TSH, T3, and T4 levels, he or she may order additional blood tests to check other factors that may indicate Graves’ disease—such as antibody levels.
Testing TSH Levels
This is usually the first test the doctor orders. He or she will want to check on your thyroid-stimulating hormone level.
If you have Graves’ disease, your thyroid-stimulating hormone (TSH) level will probably be very low because the pituitary gland will try to compensate for the excess T3 and T4 hormones in the blood. It’ll stop producing TSH in an attempt to stop production of the thyroid hormones.
Testing Total T3 and T4 Hormone Levels
If your TSH level is very low, the doctor may want to also check your T3 and T4 hormone levels as he or she works towards a diagnosis of Graves’ disease.
Normal ranges of T3 and T4 are needed to regulate your body’s metabolism at the cellular level, so in the blood test, your doctor will be looking for abnormal levels.
People with Graves’ disease will usually have too much T3 and T4 in their blood. That’s because the antibody thyroid-stimulating immunoglobulins (TSI) are misdirecting the thyroid to make too much T3 and T4. You can read more about TSI and how it causes this condition in our basic article on Graves’ disease.
Testing Free T4 Hormone Levels
A free T4 is another type of blood test run if your TSH is not normal. It is a newer test than the total T4. Results from a total T4 (as described above) may be altered by blood proteins that bind to the T4 hormone.
However, a free T4 is less affected by blood proteins and reveals a more accurate picture of thyroid function or dysfunction. A free T4 may be recommended when you have a goiter, as in some cases of Graves’ disease.
Thyroid-stimulating immunoglobulin (TSI) is a type of antibody (immunoglobulin) measured from drawn blood. TSIs can bind to tissues in the eyeballs and beneath the skin and contribute to the development of exophthalmos (bulging eyes) and pretibial myxedema (skin thickening on the front of the lower legs). You can read our article on these possible symptoms of Graves’ disease to learn more.
Checking the TSI level is done if the doctor can’t definitively diagnose Graves’ disease from your symptoms and TSH, T3, and T4 levels.
Testing Thyroid Peroxidase Antibodies (TPO) Level
Since Graves’ disease is an autoimmune disorder (where your immune system attacks healthy body tissue), this blood test may be recommended. TPO measures the level of thyroid peroxidase antibodies. If you have those antibodies in your blood, it suggests that the immune system has attacked the thyroid. However, about 5-10% of healthy people test positive for TPO antibodies, so the presence of these antibodies doesn’t always indicate that you have an autoimmune disorder.
Radioactive Iodine Uptake (RAIU) and Scan
A radioactive iodine uptake test and scan will measure the amount of iodine your thyroid absorbs and also determine if all or only part of the thyroid is overactive. This test is usually performed in a hospital or medical center’s nuclear imaging department.
RAIU involves taking an iodine “pill” called a radioactive tracer four to six hours before your first thyroid gland scan. Iodine is used because your thyroid gland naturally absorbs iodine through your bloodstream from foods that contain the element in order to make thyroid hormone. It’s a specific test because the thyroid absorbs iodine much better than other parts of the body, especially if your thyroid is overactive.
Another scan is repeated 24 hours later. The test is not painful and requires you to lie on a padded table with your head tipped backward to fully expose your neck and thyroid area.
The amount of radioactive tracer your thyroid absorbs determines if your thyroid function is normal or abnormal. A high uptake of iodine tracer may mean you have hyperthyroidism or Graves’ disease.
Depending on your symptoms (e.g., exophthalmos), other tests may include a CT scan, MRI, or ultrasound (echography) of the eyes and eye sockets (called orbital imaging) in order to define the exact impact of Graves’ disease on the eyes and surrounding structures (e.g., muscles).
The doctor combines your medical history, symptoms, and all test results to make a diagnosis of Graves’ disease.