The thyroid is the gland that produces hormones that regulate your metabolism. It is located beneath the Adam's apple and is the only gland in the body that uses iodine to function. The thyroid gland is controlled by the pituitary and hypothalmus glands. As a group, these glands are known as endocrine glands. A specialist who manages thyroid care is an endocrinologist.
Thyroid illnesses are not uncommon and are caused by the gland either overproducing or underproducing two hormones, the T4 and the T3. A "normal" thyroid reading cannot be made without testing for at least one thyroid hormone in conjunction with the thyroid stimulating hormone (TSH), which is produced by the pituitary gland.
When testing for levels of T4 hormone, your physician will order a blood test called either a Total T4 or a Free T4. Using a Total T4 test, a number between 4.5 and 12.5 is considered normal. Using the Free T4 test, the normal range is 0.7-2.0.
This test should be combined with the TSH and T3 tests to get a clear picture of the condition.
When testing for levels of the T3 hormone, your physician will order a blood test called either a Total T3 or Free T3. Using the Total T3 test, the normal range is 60-181. Using the Free T3 test, a number between 230-420 is considered normal.
This test should be combined with the TSH and T4 tests to get a clear picture of the condition.
A TSH test measures the amount of TSH produced by the pituitary gland. This is also a blood test. The normal range for TSH is between 0.5 and 5.0. However, clinical tests done in the early 2000s showed that some people with readings at the 5.0 level actually had underactive thyroids. Because of this, some physicians use a scale of 0.3-3.0 when determining the normal range.
It is important to note, as above, that the TSH test is merely an indicator and is not conclusive enough to be considered alone and should be combined with tests for T4 and/or T3 levels.
What Does this Mean?
Because testing for production of T4, T3 or TSH individually is not enough to determine a specific thyroid issue, it is critical that these tests be combined. The pituitary gland produces TSH and may register at high levels if no or not enough T4 is being produced or lower levels if too much T4 is being produced. In addition, the level of TSH in the bloodstream may be an indication of a pituitary gland problem rather than a thyroid issue. Therefore, these results must be considered together.
A patient may be diagnosed with hyperthyroidism, also known as Graves' disease, or an overactive thyroid if test results show high levels of T4 and low levels of TSH. Symptoms of hyperthyroidism include weight loss, increased bowel movements, irritability, sleeplessness or nervousness. Hyperthyroidism may be regulated in the short term with drug therapy and in the long term through surgery or a radioactive treatment to destroy a portion of the thyroid gland.
A patient may be diagnosed with hypothyroidism, or an underactive thyroid, if test results show low levels of T4 and high levels of TSH. Symptoms of hypothyroidism include fatigue, weight gain and lack of motivation. Hypothyroidism is easily regulated with drug therapy.