In addition to conducting a physical examination and taking your unique symptoms into account, your doctor will use one or more laboratory tests to diagnose Hashimoto's thyroiditis. This article will cover the 3 most common diagnostic tests that detect this common thyroid disorder: the thyroid-stimulating hormone test, anti-thyroid antibodies tests, and the free T4 hormone test.
Thyroid-stimulating Hormone Test
A thyroid-stimulating hormone (TSH) test is a blood test that is one of the go-to tests for diagnosing hypothyroidism. Remember, Hashimoto's thyroiditis is the most common cause of hypothyroidism.
Thyroid-stimulating hormone is not produced by your thyroid—it's produced by your pituitary gland in your brain. When the pituitary detects even the slightest decrease in thyroid hormone production, it releases a greater amount of TSH to encourage the thyroid gland to make more hormones.
The goal of the TSH test is to determine whether your TSH levels are within the normal range. If they are higher than they should be, this may indicate Hashimoto's thyroiditis (and, in turn, hypothyroidism). Remember, higher TSH levels mean that your brain thinks the thyroid is not producing enough hormones and needs stimulation (the "S" in TSH) to make more. Thyroid-stimulating hormone ranges are unique to each patient, and your doctor will determine your healthy TSH range.
You can read more about the thyroid-stimulating hormone test in our article about hypothyroidism diagnosis.
Anti-thyroid Antibodies Tests
Anti-thyroid antibodies (ATA) tests, such as the microsomal antibody test (also known as thyroid peroxidase antibody test) and the anti-thyroglobulin antibody test, are commonly used to detect the presence of Hashimoto's thyroiditis.
Hashimoto's thyroiditis is an autoimmune disorder, and these types of disorders are caused by immune system malfunction. In other words, instead of protecting the body's healthy tissues, malfunctioning immune cells actually attack them.
When immune cells attack your thyroid gland, which is the case with Hashimoto's thyroiditis, antibodies are produced. Anti-thyroid antibodies tests detect the presence of these antibodies and measure their levels. This test is commonly used to confirm or exclude Hashimoto's thyroiditis as the reason for hypothyroidism.
Free T4 Test
Thyroxine, or T4, is the active thyroid hormone in the blood, and your doctor may measure the level of free T4 in your bloodstream to help confirm a Hashimoto's thyroiditis diagnosis. Free T4 is the portion of total T4 thyroid hormone that is available to your tissues. Typically, in Hashimoto's thyroiditis, the pituitary gland in the brain will make more TSH (your blood test for TSH comes back high) because it thinks the thyroid is not making enough thyroid hormone. (Your T4 blood test may be below normal or on the low end of normal).
If your TSH test comes back normal, but your symptoms resemble those of hypothyroidism, a free T4 test may help reveal any thyroid hormone problems. Low levels of free T4 indicate some deficiency in thyroid hormone production, even if your TSH levels are normal.
There are numerous tests available today that your doctor may use to help diagnose Hashimoto's thyroiditis. If you notice any of the symptoms of Hashimoto's thyroiditis—or if you have risk factors associated with this thyroid disorder—don't hesitate to discuss testing options with your doctor.