Diagnosis

In general, your doctor may test for Hashimoto's disease if you're feeling increasingly tired or sluggish, have dry skin, constipation, and a hoarse voice, or have had previous thyroid problems or a goiter.

Diagnosis of Hashimoto's disease is based on your signs and symptoms and the results of blood tests that measure levels of thyroid hormone and thyroid-stimulating hormone (TSH) produced in the pituitary gland. These may include:

• A hormone test. Blood tests can determine the amount of hormones produced by your thyroid and pituitary glands. If your thyroid is underactive, the level of thyroid hormone is low. At the same time, the level of TSH is elevated because your pituitary gland tries to stimulate your thyroid gland to produce more thyroid hormone.
• An antibody test. Because Hashimoto's disease is an autoimmune disorder, the cause involves production of abnormal antibodies. A blood test may confirm the presence of antibodies against thyroid peroxidase (TPO antibodies), an enzyme normally found in the thyroid gland that plays an important role in the production of thyroid hormones. But the TPO antibody test isn't positive in everyone with Hashimoto's thyroiditis. Many people have TPO antibodies present, but don't have a goiter, hypothyroidism or other problems.

In the past, doctors weren't able to detect an underactive thyroid (hypothyroidism), the main indicator of Hashimoto's disease, until symptoms were fairly advanced. But by using the sensitive TSH test, doctors can diagnose thyroid disorders much earlier, often before you experience symptoms.

Because the TSH test is the best screening test, your doctor will likely check TSH first and follow with a thyroid hormone test if needed. TSH tests also play an important role in managing hypothyroidism. These tests also help your doctor determine the right dosage of medication, both initially and over time.