Dr. MJ Bazos MD, Patient Handout

The influence of the thyroid gland is both far-reaching and critical to normal body function. It affects heart rate, cholesterol level, body weight, energy level, muscle strength, skin condition, vision, menstrual regularity, mental state and a host of other conditions. Despite its pervasive influence, however, the thyroid gland and its disorders are still not widely understood among the general public.

The thyroid is a butterfly shaped gland which wraps around the front part of the windpipe just below the Adam's apple. It produces hormones that regulate the body's metabolism and organ function. Thyroid hormone influences essentially every organ, every tissue and every cell in the body.

The most common thyroid disorder is an underactive thyroid, or hypothyroidism. This results when the thyroid fails to produce enough hormone. Less frequently, an overactive thyroid condition, or hyperthyroidism, occurs when the thyroid produces more thyroid hormone than is needed. If properly treated, patients with thyroid disorders lead normal, active lives. When left untreated, however, thyroid disorders can affect the patient's cardiovascular system, reproductive system and other major organs.

How the Thyroid Functions

The thyroid gland operates as part of a feedback mechanism involving the hypothalamus and the pituitary gland. First, the hypothalamus sends a signal to the pituitary gland through a hormone called TRH (thyrotropin releasing hormone). When the pituitary gland receives this signal, it releases TSH (thyroid stimulating hormone) to the thyroid gland. Upon receiving TSH, the thyroid responds by releasing two of its own hormones, T4 and T3, which then enter the bloodstream and affect the metabolism of the heart, liver, muscle and other organs. T4 is the main hormone released by the thyroid. T3 is made in the tissue after T4 to T3 conversion. Finally, he pituitary "monitors" the level of thyroid hormone in the blood and increases or decreases the amount of TSH released, which then changes the amount of thyroid hormone in the blood.


A Johns Hopkins University study published in the Journal of the American Medical Association proposes routine testing for mild thyroid failure among the general adult population. It concluded that periodic screening men and women 35 and older at regular intervals is as cost-effective a health strategy as screening for more common medical conditions such as high cholesterol or high blood pressure. In making this determination, the study involved the use of the test widely considered to provide the most accurate measure of thyroid gland activity the sensitive thyroid-stimulating hormone (TSH) test.

In the past, doctors were unable to detect thyroid disorder until a patient's symptoms were fairly advanced. With the sensitive TSH test, however, physicians are able to diagnose thyroid disorders at an earlier stage in many cases, even before patients begin to experience symptoms. TSH tests, due to their high degree of sensitivity, enable physicians to detect even slight abnormalities in thyroid function. Early detection and treatment of thyroid disorder allows physicians to prevent the onset of disease symptoms and curb potential organ effects for their patients.

Prior to the introduction of the TSH test, the standard blood tests or thyroid disorders measured the levels of thyroid hormones (T4 and T3) in the blood. Research showed, however, that these hormone levels could be within the normal range even when the thyroid was not functioning normally. The TSH test offers a marked advance by identifying the amount of thyroid-stimulating hormone produced by the pituitary gland, the organ that signals the thyroid gland to produce more or less T4 and T3 based on the body's need. In effect, the TSH test takes advantage of the "wisdom" of the pituitary gland, the organ that first recognizes thyroid dysfunction, and therefore provide a more exact measure of thyroid failure.

A TSH test is administered by drawing a small blood sample and sending it to a laboratory for analysis. The laboratory will read the level of TSH, and based on a reported normal value range, it will determine whether the level is below normal (hyperthyroid), above normal (hypothyroid) or within the normal range (euthyroid).

People who believe they may have a thyroid disorder should ask their primary care physician or an endocrinologist to have their TSH level assessed. In support of this precise tool for measuring thyroid activity, the American Association of Clinical Endocrinologists released clinical practice guidelines strongly advocating the use of TSH tests for diagnosing thyroid conditions.

Beyond disease diagnosis, TSH tests play a critical role in helping physicians manage thyroid disorders. In this capacity, TSH tests are used to determine precise medication treatment dosages for patients with hypothyroidism and hyperthyroidism, as well as to monitor changes in dosage requirements over time.