The thyroid is the gland in your body that regulates metabolism. It produces two hormones--T4 and T3. The normal reading for the Total T4 is considered to be between 4 and 11. However, the T4 level alone does not indicate whether you have a thyroid problem. The test must be combined with a test for TSH (thyroid stimulating hormone).
Since your thyroid regulates your metabolism, symptoms of an overactive thyroid include sleeplessness, irritability, nervousness, weight loss and increased bowel movements. Symptoms of an underactive thyroid include fatigue, weight gain and lack of motivation. A test outside of the normal ranges may also indicate thyroid cancer.
What Is T4
T4 is a thyroid hormone that has four iodine units. Iodine is used by the thyroid in production of thyroid hormone and is ingested through the foods we eat. There is more T4 in your body than T3, but it is T3 that is the active hormone.
If you believe you have a thyroid issue, ask your physician to recommend a specialist, known as an endocrinologist. These doctors specialize in issues with the endocrine glands (hormone-production glands) and are better equipped to help you manage a thyroid problem than a general practice physician. He or she will test your T4 thyroid levels as well as T3 and TSH.
If you suspect that you have an overactive thyroid, your T4 thyroid level and TSH hormones may be tested simultaneously. Your physician may order a test called Total T4 or Total Thyroxine. If the results show that your Total T4 thyroid level is above the normal range (4-11) and that your TSH is below the normal range (.5-5.5), then you may have an overactive thyroid. This is also called hyperthyroidism.
Using a test called Free T4, the normal range is .8-1.8. If your test indicates T4 thyroid level is above 1.8, you may have an overactive thyroid.
Using the Total T4, test results that show your T4 thyroid level is below the normal range (4-11) and that your TSH is above the normal range indicate an underactive thyroid. This is known as hypothyroidism.
Using the Free T4 test, if your result is less than .8, then you may have an underactive thyroid.
If you are diagnosed with an overactive thyroid, treatments include drug therapy, surgery or radioactive iodine. The latter two will reduce the size of the thyroid gland, in turn reducing the amount of T4 output. Drug therapies may help to inhibit the production of thyroid hormones, but are not usually considered a long-term solution. With the surgical option, all or part of the thyroid is removed. With the radioactive iodine option, you will ingest the radioiodine and, over the course of weeks or months, it will destroy all or part of the thyroid. Neither the surgical option nor the radioiodine option is an exact science and many patients end up with an underactive thyroid, which is then regulated through medication.
If you are diagnosed with an underactive thyroid (or end up that way after removal of the thyroid gland), you will be prescribed a hormone replacement drug that is to be taken daily for the rest of your life.