What are thyroid function tests?
Thyroid function tests, also called thyroid tests or thyroid symptom tests, show how well your thyroid gland is working. These tests are often used to diagnose an underactive (hypothyroidism) or overactive (hyperthyroidism) thyroid. Your provider may recommend them if you have a family history of thyroid disease or if you need monitoring after thyroid treatment, like medication, radioactive iodine therapy, or surgery.
At Penn Medicine, endocrinologists, radiologists, and lab specialists work together to provide accurate testing and clear explanations, so you know what your results mean and what comes next.
Do I need thyroid function testing?
Your provider may recommend thyroid function testing if you have symptoms like fatigue, unexplained weight changes, hair loss, or rapid heartbeat. Because thyroid symptoms can have many causes, these tests are often the first step in finding out if your thyroid is the source of the problem. Your provider may also suggest testing if you have a family history of thyroid disease, have other autoimmune disorders, or have had previous radiation to the neck, even if you don’t have clear symptoms.
People already diagnosed with a thyroid condition may need regular testing to monitor their health. This regular testing helps your provider confirm that your medication and treatment are working effectively.
Types of thyroid tests and what to expect
Most thyroid function tests are quick, safe, and done on an outpatient basis. The type of test you have depends on your symptoms and what your provider needs to measure about your thyroid gland function.
Blood tests, taken from a small sample of blood from your arm, are the most common way to check thyroid function. A thyroid blood panel, sometimes called a thyroid panel, may include:
- TSH blood test (thyroid-stimulating hormone): Often the first test ordered, this shows if your thyroid is making too much (hyperthyroidism) or too little (hypothyroidism) hormone.
- Free T4 (thyroxine): The T4 test measures the main hormone made by the thyroid and helps assess how well the gland is working.
- Total T3 or Free T3: The T3 test measures levels of triiodothyronine to help diagnose hyperthyroidism.
- Thyroid antibody test: This test detects antibodies that may signal an autoimmune thyroid disease.
If your provider needs to look at the structure of your thyroid, an imaging test may be recommended. These tests are painless, and you’ll usually lie still on a table while the images are taken. The most common is a thyroid ultrasound, which uses sound waves to create images of the thyroid gland and detect nodules or growths.
These tests use a small, safe amount of radioactive material to capture detailed images of your thyroid. They take longer than blood or imaging tests but are still painless and safe.
The most common is the thyroid uptake test, also called a radioactive iodine uptake test (RAIU). For this test, you’ll swallow a pill that contains a tiny amount of radioactive iodine. The iodine collects in your thyroid, and scans are usually taken twice—a few hours after you take the pill and again about a day later. During each scan, you’ll lie on a table while a special camera moves over your neck to measure how much iodine your thyroid absorbs. This helps diagnose conditions like hyperthyroidism.
Understanding your thyroid test results
No recovery time is needed for most thyroid function tests. After testing, you can return to your usual activities right after a blood draw or imaging scan. If you have a nuclear medicine test, your care team may give you special instructions like drinking extra fluids to help clear the small amount of radioactive material from your body.
When your results are ready, your provider will review them. If the tests show abnormal hormone levels, they may order additional tests to pinpoint the exact cause of the problem. Thyroid function tests provide important information that can help diagnose conditions like:
- Hyperthyroidism (overactive thyroid)
- Hypothyroidism (underactive thyroid)
- Thyroiditis
- Hashimoto’s disease
- Graves’ disease
- Postpartum thyroiditis
Trusted specialists in thyroid testing and management
Having your thyroid function tested is only the first step. It’s just as important to have experts who can interpret the results and guide your care. At Penn Medicine, your testing is overseen by specialists in endocrinology, radiology, nuclear medicine, and pathology. We use advanced labs and imaging technology to give you accurate results, often within a short time. Our team also explains what your results mean and connects you to the right treatment if needed.
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