What Tests are Used to Diagnose a Thyroid Condition?

Diagnosis of Hypothyroidism, Thyroid Cancer and More

Blood tube sitting on blood results with technician at microscope in lab
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In addition to a thyroid-specific clinical evaluation, thyroid conditions require specific tests and procedures to confirm diagnosis. The following article reviews the different criteria for diagnosis.


To help diagnose or rule out hypothyroidism, doctors will typically start with the blood test that measures thyroid-stimulating hormone (TSH). As of Spring 2003, most American laboratories had a normal range from around 0.5 to 5.5. However, the American Association of Clinical Endocrinologists has recently recommended that the normal range be revised to 0.3 to 3.0. With 5.5 as the top end of the normal range, a TSH above that level is considered hypothyroid. Under the newer guidelines, however, a TSH above 3.0 could be diagnosed as hypothyroid.

Note: Some practitioners believe that TSH levels should be maintained at lower levels during pregnancy. (See What Are The Normal TSH Ranges During Each Trimester of Pregnancy?)

Other blood tests that may be done to help diagnose hypothyroidism include:

  • Total T4 (Total Thyroxine) - a low Total T4 level along with an elevated TSH may indicate hypothyroidism.
  • Free T4 (Free Thyroxine) - a low Free T4 level along with an elevated TSH may indicate hypothyroidism.
  • Total T3 (Total Triiodothyronine) - a low Total T3 level along with an elevated TSH may indicate hypothyroidism.
  • Free T3 (Free Triiodothyronine)- a low Free T3 level along with an elevated TSH may indicate hypothyroidism.

Hashimoto's Disease

Hashimoto's thyroiditis is the autoimmune disease that is the most common cause of hypothyroidism. The characteristic Hashimoto's thyroiditis patient would have high TSH values and low T3 and T4 (or Free T3 and Free T4) levels.

A high concentration of thyroid autoantibodies - Anti-TPO antibodies in particular - is also characteristic of Hashimoto’s disease.

Graves' Disease and Hyperthyroidism

Diagnosing hyperthyroidism requires a complete clinical evaluation, during which the doctor examines the patient and the thyroid. Hyperthyroidism can usually be confirmed by use of the TSH, T4 (or Free T4), T3 (or Free T3) and Radioactive Iodine Update (RAI-U) tests. The Radioactive Iodine Update (RAI-U) test, which visualizes the thyroid and its ability to absorb iodine, is also used to diagnose hyperthyroidism, and help determine whether the hyperthyroidism was caused by Graves' disease. Diagnosing Graves' disease also frequently involves evidence of elevated Thyroid Receptor Antibodies (TRAb) / Thyroid-Stimulating Immunoglobulins (TSI).

A comprehensive overview of how Graves' disease and hyperthyroidism is diagnosed is featured in this article: Diagnosis of Graves' Disease/Hyperthyroidism.


Several steps can be involved in diagnosing goiter:

  • Examining and observing your neck enlargement
  • A blood test to determine if your thyroid is producing irregular amounts of thyroid hormone
  • Antibodies testing, to confirm that autoimmune disease that may be the cause of your goiter
  • An ultrasound test to evaluate the size of the enlargement
  • A radioactive isotope thyroid scan to produce an image of the thyroid and provide visual information about the nature of the thyroid enlargement (note: because of potential damage to the baby's thyroid, these are not done during pregnancy or breastfeeding)


Nodules are usually evaluated by the following methods:

  • A blood test, to determine whether your nodules are producing thyroid hormone
  • Radioactive Iodine Uptake (RAI-U)
  • An ultrasound of your thyroid, to determine whether the nodule is solid or fluid-filled
  • A fine-needle aspiration or needle biopsy of your nodules, to evaluate whether the nodule(s) may be cancerous

Since 2011, a specialized fine needle aspiration process has been available, which eliminates indeterminate and inconclusive FNA biopsy results. This test is called the Veracyte Afirma Thyroid Analysis.

Thyroid Cancer

Thyroid cancer diagnosis can involve a number of procedures and tests, including a physical exam, biopsy, imaging tests, and blood tests. This article provides an overview of the diagnosis process.

In general, however, for everyone except pregnant patients, an RAI-U is done in order to help identify if the nodules are cold, which means they have a greater potential to be cancerous.

If a nodule is suspected of being cancerous, a fine needle aspiration (FNA) biopsy is conducted. Fluid and cells are removed from various parts of the nodule, and these samples are then evaluated by a pathologist. Between 60 and 80 percent of FNA tests show that the nodule is benign. Only about one of 20 FNA tests reveals cancer. The remainder of cases are classified as "suspicious." Typically, suspicious nodules are surgically removed for biopsy, to rule out or diagnose cancer.

View Article Sources
  • Braverman, MD, Lewis E., and Robert D. Utiger, MD. Werner and Ingbar's The Thyroid: A Fundamental and Clinical Text. 9th ed., Philadelphia: Lippincott Williams & Wilkins (LWW), 2005.