The thyroid gland lies at the base of the neck. It secretes several hormones. These hormones regulate cell activity throughout the body. The main one is called thyroxine. Several disorders can cause the thyroid to produce too much or too little. Hyperthyroidism is too much hormone. Hypothyroidism is too little hormone. These conditions can result from inflammation, cysts, or cancer of the thyroid. A goiter is an enlarged or swollen thyroid gland. Symptoms in a hyperthyroid person include:
* goiter and/or protruding eyes,
* heat intolerance,
* diarrhea,
* rapid pulse.

Symptoms in a hypothyroid person develop more slowly and include:
* drooping eyelids,
* constipation,
* cold intolerance, and
* decreased concentration.

A group of tests measure blood levels of various forms of thyroid hormones. The tests often include thyroid stimulating hormone, or TSH, which comes from the pituitary gland. These tests require drawing a blood sample from the arm.

If the thyroid is enlarged or lumpy, a doctor may order a thyroid biopsy. This procedure removes some thyroid tissue with a hollow needle under local anesthetic. Occasionally, the person undergoes open biopsy under general anesthetic. Analysis in a lab can detect cancer or other problems.

Another procedure is the radioactive iodine uptake test. Thyroid tissue absorbs iodine from the body very quickly. The patient swallows a small amount of radioactive iodine. This tests measures the amount that collects in the gland after 6 to 24 hours. This can accurately diagnose hyperthyroidism. It is less accurate for hypothyroidism. The test is painless and the small amount of radioactivity is harmless. A thyroid scan produces an image of the thyroid 24 hours after the person swallows radioactive iodine. A camera scans the neck for about 30 minutes and detects low levels of radiation.

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