Thyroid Stimulating Hormone - TSH Blood Test

Thyroid is the butterfly-shaped gland located in front of the windpipe (on the anterior side of the neck), just below the thyroid cartilage. This gland produces hormones, mainly thyroxine (T4) and triiodothyronine (T3). Another hormone known as calcitonin, is also produced by the thyroid gland. This hormone helps in maintaining the required level of calcium in the body. The main functions of the thyroid gland is to maintain the rate of metabolism of the body and growth. It can also affect the rate of functioning of other systems. All these are achieved through the action of hormones produced by this gland.

The thyroid gland is controlled by the hypothalamus in the brain and the pituitary gland. The hypothalamus releases thyrotropin-releasing hormone (TRH), which induces the pituitary gland to release thyroid-stimulating hormone (TSH). TSH regulates the hormone-production of the thyroid gland. A low level of T3 and T4 in the blood, stimulates the pituitary to produce more TSH and vice versa. Hence, evaluating the blood level of TSH can help in assessing the functioning of the thyroid gland.

The most common problems related to the functioning of the thyroid gland are hyperthyroidism and hypothyroidism. Hyperthyroidism denotes an overactive thyroid gland characterized by an excess of thyroid hormones and hypothyroidism refers to an under active thyroid gland with deficient hormones. A person suffering from hyperthyroidism may experience symptoms like rapid heart beats, weight loss, nervousness, irregular menstrual periods, diarrhea, etc, whereas hypothyroidism can cause symptoms like frequent menstrual periods, weight gain, fatigue, constipation and dry skin.

The TSH blood test is suggested by doctors, for those people who experience the symptoms of either hyperthyroidism or hypothyroidism. This test may be advised for people with an enlarged thyroid gland or to monitor the results in those who are already undergoing treatment for any thyroid problems. This test is also a part of the newborn screening program in the United States. Some medical organizations suggest this test for women above the age of 35, whereas some others recommend the test for women above 65 and men above 70.

The normal blood level of thyroid stimulating hormone in adults is between 0.4 and 5.0 uIU/mL(micro international unit per milliliter), but the desirable level for patients undergoing treatment (for thyroid problems) is between 0.3 to 3.0 mIU/L. The normal TSH level for kids ranges between 1.3-19 uIU/mL for normal infants at birth, 0.6-10 uIU/mL at 10 weeks, 0.4-7.0 uIU/mL at 14 months and gradually dropping to reach 0.4-4.0 uIU/mL as they become adults.

For a better interpretation, the TSH levels are evaluated along with the levels of T3 and T4 (thyroid hormones) in the blood. A blood test showing abnormal levels of TSH, may not help the doctor to determine the reason for the problem. Hence, the levels of T3 and T4 are also checked. It is primarily a thyroid disease, if a person has high levels of TSH and low levels of T3 and T4,and vice versa. If both TSH and thyroid hormones are either low or high, then the problem is primarily related to the pituitary gland.

There are some factors, which can interfere with the results of the test. One of them is drugs containing aspirin. If you are already taking some medicines, inform your doctor before the test. Some diseases or medical conditions, X-ray with iodine dye or test using radioactive materials or extreme stress can also affect the level of TSH in the blood. TSH level may also be low during the first stages of pregnancy. This test is done by collecting a small amount of blood with a syringe. This blood is then sent to a laboratory for conducting the test.

Generally, no risks are associated with this simple test, and those experience the symptoms discussed above, can consult their doctor and take this test.