The thyroid is a gland that sits at the base of the neck below the voice box, or larynx. It is part of the endocrine system, and is responsible for producing key hormones that regulate the body's metabolism. When the thyroid gland malfunctions, it can trigger effects that cause significant disruptions in a number of organ systems. Abnormal thyroid readings are a main way of determining which particular malfunctions are affecting a given individual.

Hyperthyroidism

According to the nonprofit Hormone Foundation, your thyroid may malfunction in a number of different ways. If tests performed by an endocrinologist (hormone and endocrine specialist) reveal abnormally high levels of thyroid hormone, you may be suffering from a condition called hyperthyroidism. Symptoms of hyperthyroidism include fatigue, rapid heartbeat, weight loss, muscle weakness, diarrhea and menstrual cycle disruptions. The most likely cause of your hyperthyroidism is called Graves' disease, which occurs when antibodies from your immune system mistakenly attack your thyroid gland, forcing it to produce excess hormones. If you have Graves' disease, your symptoms may also include swelling behind your eyes that causes them to bulge or press forward.

Hypothyroidism

If you have abnormally low levels of thyroid hormones, you may suffer from an underactive thyroid gland. This condition is called hypothyroidism. Symptoms of hypothyroidism include weight gain, fatigue, depression, constipation, sluggishness, dry hair and skin and menstrual cycle irregularities. If your hypothyroidism is severe, you may be additionally diagnosed with a condition called myxedema. In some individuals with myxedema, the presence of infections, injury or the common cold may bring about life-threatening complications including coma and dangerously lowered body temperature (hypothermia).

Thyroid Nodules

Thyroid testing may also reveal the presence of abnormal nodules within your thyroid gland. These nodules typically manifest as either growths of your thyroid tissue or as fluid-filled cysts. Thyroid nodules are quite common, and as a rule they do not pose any real health risks. However, if your nodules are larger than half an inch in diameter, your doctor may want to investigate them further and see if they indicate the presence of a more dangerous condition such as cancer. To determine the seriousness of your thyroid nodules, your doctor may order a tissue sampling procedure called a biopsy. If the results of a biopsy indicate that your nodules are benign (non-cancerous), you will likely need to see your doctor at regular intervals to make sure that no dangerous changes occur at a later date. If your thyroid nodules are malignant (cancerous), you will likely undergo surgical removal of all or part of your thyroid gland. Doctors may also perform surgery if they cannot determine through other testing whether a nodule is malignant. Consult your endocrinologist for additional information on the results of thyroid testing. Consult your surgeon if testing reveals the presence of malignant nodules.

Source:

The Hormone Foundation

Lab Tests Online

The Mayo Clinic

Resource:

American Thyroid Association-ATA Patient Education Web Brochures

U.S. National Library of Medicine-National Institutes of Health: Thyroid Diseases