Thyroid gland is endocrine gland, responsible for the production of thyroid hormones, known as the T3 and T4. The main role of thyroid hormones is to regulate metabolism of our body. Hyperthyroidism and thyrotoxicosis are condition of increased production of thyroid hormones, and they might cause anxiety, diarrhea, sleeping difficulties, heart problems, tremor and muscle weakness. Tests are usually done for T4 hormone (thyroxine), since there is much more T4 than T3 in the blood (about 80% is T4). Measuring the elevation of T4, we can check the normal function of the thyroid gland in general.
T4 TestsThe way to check your normal T4 levels is to perform a blood test or radioimmunoassay (RIA, or T7 test). The preferred method is T7 test, simply because it doesn’t get false results as the blood test, if the person used some medications (such as thyroid drugs, Aspirin or contraceptive pills). With this test, lab can define the amount of T4 present in your blood. Most doctors would advise you not to take any medications before taking this T7 test, especially if you are a woman, since they might (slightly, but still might) affect the results of the blood testing.
T4 ResultsAs normal T4 levels, doctors recognize 4.8 to 10.4 mcg/dl of the blood. Sometimes, there is a number representing the free T4 level, which should be between 0.8 and 1.7 mcg/dl. If the T4 level is from 0.5 to 5.5 mcg/dl doctors say that it is a lower T4 level, and for more than 11 mcg/dl of T4 in the blood they say it is a high T4 level. Overactive thyroid gland is presented with the heightened levels of T4 in the blood. Possible causes of hyperthyroidism are: iodine, Graves’ disease, thyrotoxicosis, pituitary adenoma and other. Hypothyroidism is characterized by the amount of T4 lower than normal. Underactive thyroid gland and insufficient stimulation of the thyroid gland are the potential causes of this disorder. Either way, results above or under the normal level of T4 suggest that thyroid gland is not functioning properly or there might be some problem with the pituitary gland. In extremely rare cases, patients have problem with glands, pituitary and thyroid. If suspecting for the pituitary problem, doctor will order TSH (thyroid stimulating hormone, associated with the pituitary gland) blood test. The results of this test will confirm or rule out possible problem with pituitary gland. Always consult your doctor about the results of your blood tests. S/he will advise the required measures and suggest the treatment if necessary.