The thyroid gland, a part of the body's endocrine system, lies at the front of the neck and below the Adam's apple. This small, butterfly-shaped organ is responsible for releasing hormones that serve as some of the body's chemical messengers. When a person's thyroid produces too much hormone, the result is hyperthyroidism, while the production of too little thyroid hormone causes hypothyroidism. Both of these conditions can cause uncomfortable and potentially dangerous symptoms. Your doctor can use the results of thyroid blood tests to determine if your thyroid level numbers are within a normal range.
Thyroid Testing
Physicians commonly use blood tests to measure TSH, or thyroid stimulating hormone; T3, or triiodothyronine; and T4, or thyroxine. TSH testing can reveal whether the thyroid, or in some cases, the pituitary gland, is functioning normally. Testing for T3 and T4 measures the amount of the hormones the thyroid gland is producing and sending throughout the body. Normal value ranges may vary somewhat, depending on the laboratory handling the testing.
TSH Ranges
For a person who has no symptoms of either an overactive or underactive thyroid, normal values from a TSH test range from 0.4 to 4.0 mIU/L, or milli-international units per liter. If you are taking medication for thyroid disease, TSH results ranging between 0.5 and 2.0 mIU/L indicate that you are being treated appropriately, according to the UCLA Endocrine Surgery website. However, if your TSH value is over 2.0 mIU/L, you may show no signs of an underactive thyroid, but are apt to develop hypothyroidism, and as such, you physician should monitor you.
T3 Ranges
The normal range for a T3 test is between 100 to 200 ng/dL, or nanograms per deciliter. T3 levels may elevate due to higher than normal levels of a protein that carries T3 in the blood. This can happen due to pregnancy, use of estrogen or birth control pills, liver disease or an inherited condition. Lower than normal T3 levels can be the result not just of hypothyroidism, but of illness or starvation.
T4 Ranges
The normal range for a T4 test is between 4.5 to 11.2 mcg/dL, or micrograms per deciliter. High levels of T4 in combination with low levels of TSH can indicate an overactive thyroid, which may be caused by such conditions as Graves disease or thyroiditis. Low T4 levels can be indicative of hypothyroidism, illness or malnutrition. Certain drugs such as birth control pills, estrogens or methadone can increase T4 levels, while drugs such as androgens, anabolic steroids and lithium can cause a decrease in T4.
