Doctors check your thyroid through a combination of a physical neck exam, blood tests, and sometimes imaging or a biopsy. The process usually starts simple and gets more detailed only if early results suggest a problem. Most people only need a blood draw and a quick feel of the neck to get a clear picture of how their thyroid is working.
The Physical Exam
Your doctor will feel your neck with their fingers, a process called palpation. You’ll be seated or standing while they press gently on the front of your lower neck, searching for the thyroid gland, which sits just below the Adam’s apple. They may stand in front of you or behind you, using both hands to feel each side of the gland.
During the exam, you’ll be asked to swallow a sip of water. The thyroid moves upward when you swallow, which helps the doctor feel its shape and size more clearly. They’re checking for several things at once: whether the gland feels enlarged, whether there are any lumps (nodules), how firm or soft the tissue is, whether it’s tender, and whether it moves normally. They’ll also feel the lymph nodes in your neck for anything unusual.
A thyroid that’s more than twice its normal size, or that bulges visibly at the sides of the neck, is classified as a goiter. But many thyroid problems don’t cause any visible or noticeable changes in the neck, which is why blood work is almost always the next step.
Blood Tests: TSH Comes First
The single most important thyroid test is TSH, or thyroid-stimulating hormone. This is a hormone made by the pituitary gland in your brain, and it acts like a thermostat for your thyroid. When your thyroid isn’t producing enough hormone, the pituitary pumps out more TSH to push it harder. When your thyroid is overproducing, the pituitary dials TSH way down.
For most adults, a normal TSH falls between roughly 0.27 and 4.2 micro-international units per milliliter, though reference ranges vary slightly between labs. A TSH above the normal range suggests hypothyroidism (an underactive thyroid), while a TSH below normal suggests hyperthyroidism (an overactive thyroid). The ranges are different for children and infants, with newborns having much higher normal values, up to around 15.2 in the first five days of life.
If your TSH comes back abnormal, your doctor will typically order follow-up blood tests to get more detail. These include T4 and T3 tests, which measure the actual thyroid hormones circulating in your blood. Together, TSH and these hormone levels tell your doctor not just that something is off, but how far off it is.
Antibody Tests for Autoimmune Conditions
When blood work points to a thyroid problem, your doctor may want to know the underlying cause, not just the hormone levels. Autoimmune diseases are the most common reason for both an overactive and underactive thyroid, and specific antibody tests can identify them.
Two antibodies, thyroid peroxidase antibodies (TPOAb) and thyroglobulin antibodies (TgAb), point toward Hashimoto’s disease, the leading cause of hypothyroidism. A different antibody, thyrotropin receptor antibodies (TRAb), is a marker for Graves’ disease, the most common cause of hyperthyroidism. These are all simple blood draws, often done at the same time as your TSH and hormone panels.
Thyroid Ultrasound
If your doctor feels a lump during the physical exam, the standard next step is an ultrasound. This painless imaging test uses sound waves to create a picture of your thyroid and the surrounding lymph nodes. It shows the size of any nodules, whether they’re solid or fluid-filled, and whether they have features that look suspicious.
Ultrasound doesn’t use radiation and takes only about 15 to 30 minutes. You lie on your back with your neck extended while a technician glides a small probe over your neck. It’s worth noting that routine screening of people who feel fine and have no symptoms or suspicious exam findings is not recommended. The U.S. Preventive Services Task Force advises against screening for thyroid cancer with ultrasound in asymptomatic adults because it tends to catch tiny, harmless nodules that lead to unnecessary treatment without improving health outcomes.
Radioactive Iodine Uptake Test
This test is used specifically when blood work shows hyperthyroidism and the doctor needs to figure out why. Your thyroid uses iodine to make its hormones, so by giving you a small amount of radioactive iodine (usually as a capsule you swallow) and then scanning your neck hours later, the doctor can see how aggressively the gland is absorbing iodine. Higher-than-normal uptake is the pattern seen in Graves’ disease. Other causes of hyperthyroidism show different uptake patterns, which helps guide treatment decisions.
Fine Needle Aspiration Biopsy
When an ultrasound reveals a nodule with concerning features, a biopsy is the definitive way to check whether it’s cancerous. The procedure is called fine needle aspiration, and it’s less invasive than it sounds. The needle used is thinner than the one in a typical blood draw.
You lie on your back with your head tipped slightly backward, sometimes with a pillow under your shoulders to extend your neck. After cleaning the skin and sometimes applying a local anesthetic, the doctor inserts the thin needle into the nodule using ultrasound guidance to see exactly where the tip is going. The needle withdraws a small sample of cells, which takes only a few seconds per pass. To get a reliable sample, the doctor typically repeats this two to six times, targeting different parts of the nodule with fresh needles. If the nodule contains fluid, a syringe may be used to drain it during the same procedure. You’ll be asked to stay still and avoid talking, coughing, or swallowing while the needle is in place.
The cell samples are then examined under a microscope and graded using a standardized system called the Bethesda scale, which has six possible outcomes. The most common result, accounting for up to 70% of biopsies, is benign. Nodules in that category carry less than a 3% risk of being cancerous.
One Thing to Know Before Your Blood Test
If you take biotin supplements (also labeled as vitamin B7 or vitamin H, and found in many hair, skin, and nail formulas), stop taking them at least two days before any thyroid blood work. Biotin interferes with the lab equipment used to measure thyroid hormones, and the American Thyroid Association has flagged this as a real source of misdiagnosis. The most common effect is falsely high T4 and T3 readings combined with falsely low TSH, which can look exactly like hyperthyroidism on paper even when your thyroid is perfectly fine.