Thyroid Disease (cont.)

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How is the diagnosis of thyroid disease made?

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Blood tests

Blood tests are often used to help determine thyroid function. The level of thyroid stimulating hormone (TSH) is often a screening tool and can be used along with serum levels of T3 and T4. If these hormone levels are abnormal, further information regarding a possible cause is needed. Then, antibody levels in the blood may be diagnostic. Depending on the clinical situation, your doctor may look for specific antibodies such as:

If cancer is suspected, a thyroglobulin level may be ordered. In rare circumstances, the blood calcitonin level may be checked.

Imaging

Imaging may be performed if there is concern about the structure of the gland, if size needs to be quantified, or if there is a suspicion of cancer. Common modes of imaging include an ultrasound of the thyroid gland and radioiodine scanning and uptake. Ultrasonography helps determine size and consistency of the gland. For example, ultrasonography is good at detecting cysts or calcifications within a gland, but it cannot always distinguish a benign enlargement of the gland from a cancer. Ultrasonography may be performed in a doctor's office or in a hospital's radiology department.

Thyroid scans use radioactively labeled form of iodine and are usually performed in the radiology department of a hospital or clinic. Since the thyroid is the only tissue in the human body that picks up iodine, the scan is very specific for finding thyroid tissue. If the thyroid is not picking up iodine normally, "spots" appear on the scan. A "cold" spot implies the tissue is not picking up enough iodine compared to the rest of the gland. This may be seen in nonfunctioning nodules and may also be a sign of malignancy.

A "hot" spot implies that the tissues in that area is taking up more iodine than the surrounding tissue, and that tissue is overactive. This may be seen in a toxic nodule. Hot spots are rarely cancerous. The physician will compare the scan results to normal thyroid uptake. A normal thyroid picks up 8% to 35% of the administered dose of iodine within 24 hours. Values above or below this range may point to underlying thyroid disease.

Biopsy

A biopsy provides a tissue sample for a pathologist to analyze. Biopsy is usually the gold standard for diagnosis, especially when looking for cancer. Thyroid biopsy is usually performed using a fine needle to aspirate cells from the gland. This procedure is usually called a fine needle aspiration (or FNA). FNA can be performed in an outpatient clinic and may involve ultrasonography to help guide the needle. Biopsies can also be obtained during surgery. FNA is safe and easily performed. However, depending on the skill of the person performing the FNA, the FNA may not yield enough tissue, or the sampling may not be from an optimal area to establish the diagnosis.

Medically Reviewed by a Doctor on 8/7/2013

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