What is the normal thyroid-stimulating hormone (TSH) range at your lab?
The TSH test is the most commonly used test for diagnosis and management of hypothyroidism in the United States. But different labs often have slightly different values for what is known as the "TSH reference range." This measure is the range of test values deemed to reflect a normal population.
At the lab used by my doctor, the TSH reference range is 0.5 to 5.5 as of fall 2006. A TSH value of less than 0.5 is considered hyperthyroid (overactive thyroid), while a TSH value of more than 5.5 is considered hypothyroid (underactive thyroid). Different labs might use a lower limit of anywhere from 0.35 to 0.6, and an upper threshold of anywhere from 4.0 to 6.0. In any case, it is important for you to be aware of the reference range at the lab where your blood is sent, so you know the standards by which you are being diagnosed.
NOTE: Since late 2002, the American Association of Clinical Endocrinologists (AACE) and other professional groups have recommended a narrower TSH reference range of 0.3 to 3.0. This means that hyperthyroidism is now suspected at TSH levels below 0.3, while levels of 3.0 and above are considered potentially indicative of hypothyroidism. To learn more about these standards, check out Does Your Doctor Know About the New TSH Lab Standards?
What TSH level will you use as a target for me?
This is a loaded but important question. Your physician's answer will reveal her or his philosophy about what represents a "normal" level for TSH. Some doctors believe that getting a patient into the very top of the normal range is the objective of hypothyroidism treatment. For example, using the 5.5 TSH standard from my own lab, some physicians believe that prescribing thyroid hormone replacement medication to get a patient's TSH down to below 5.5 (even perhaps just down to 5.4) would constitute full treatment.
Physicians vary in what TSH level within the normal range they believe makes an ideal target. Some practitioners, for example, might target a TSH level between 1.0 and 2.0 based on their own experience suggesting that patients may feel best at these levels.
Other doctors closely follow the new AACE standards discussed earlier, and believe that thyroid hormone replacement treatment should target a TSH level of no more than 3.0 in hypothyroid patients.
Finally, some practitioners believe that thyroid treatment decisions should be based primarily on a patient's individual response, with TSH used mainly as a guideline. (For example, Dr. Steven Hotze, the author of "Hormones, Health and Happiness," relies on this approach in his practice, described in this interview.