Hypothyroidism is diagnosed by an elevated serum TSH and a low serum Free T4.
Most people with mild hypothyroidism which means an elevation of the TSH level of from 5 to 15, will usually not notice any symptoms. If the TSH level is elevated at from 15 to 50, most people will feel like something is wrong. And if the TSH level is higher than 50, the patient will usually know something is wrong and will go to the doctor. (1)
Although there are other medicines that can be used to treat hypothyroidism, the vast majority of doctors will prescribe T4 (there are two brands—Synthroid and Levoxyl and a number of generics—the generic name of T4 is levothyroxine).
The average dose of levothyroxine (T4) is 1.6 micrograms per kilogram of body weight each day. (2) To find your weight in kilograms you multiply your weight in pounds times 2.2. The result is your weight in kilograms.
People often ask, does the dose refer to what a person should weigh (his or her ideal body weight) or what the person actually weighs (often a lot more than the ideal body weight)?
Actually, the American Association of Clinical Endocrinology treatment guideline does not say. I estimate the ultimate replacement dose based on the ideal body weight.
Many doctors start the patient on a small dose of say 25 to 50 micrograms per day and adjust the dose every 8 weeks (it takes about 8 weeks for the thyroid tests to reach their new level). They adjust the dose based on the patient’s target symptoms (the symptoms that led the doctor and patient to suspect hypothyroidism) and based on the serum TSH level and the Free T4 level.
This gradual approach to prescribing the levothyroxine (start low and go slow) is best for elderly persons or for persons with a weak heart.
Sometimes the dose of thyroid medicine prescribed is more than the person actually needs (because each person is unique). If the dose proves to be too high, the patient can develop the symptoms of excessive thyroid hormones (hyperthyroidism).
Each patient who starts on thyroid medicine needs to learn the symptoms of hyperthyroidism (too much thyroid medicine) so that he can report the symptoms immediately and be checked before his regular checkup.
The symptoms of hyperthyroidism are increased anxiety, fast or hard heartbeat, excessive perspiration, diarrhea, fine shaking of the hands or fingers, increased fatigue, getting hot more easil, and trouble sleeping.
If a patient on levothyroxine (T4) has any of the above symptoms or other symptoms that are new or worse, she should schedule an immediate doctor visit and repeat TSH and Free T4 lab tests.
For young or middle aged persons with no health problems, Dr. Skugor will place the patient on the full dose he estimates the patient will need (1.6 micrograms per kilogram each day). He makes sure the patient knows the symptoms to watch out for—of too much thyroid medication). Using this method it takes less time (and fewer visits and lab tests) to get the patient on the right dose. (3)
(1) The Cleveland Clinic Guide to Thyroid Disorders. 2009. Mario Skugor MD, p. 14.
(2) AMERICAN ASSOCIATION OF CLINICAL ENDOCRINOLOGISTS MEDICAL GUIDELINES FOR CLINICAL PRACTICE FOR THE EVALUATION AND TREATMENT OF HYPERTHYROIDISM AND HYPOTHYROIDISM. 2006 amended version available at https://www.aace.com/files/hypo-hyper.pdf
(3) The Cleveland Clinic Guide to Thyroid Disorders. 2009. Mario Skugor MD, p. 31.