What are normal TSH levels?Thyroid Stimulating Hormone (TSH) is produced by your pituitary gland and is the gas pedal for your thyroid. When your pituitary wants your thyroid to produce more thyroid hormone (thyroxine 4, aka T4) is will press on the gas pedal (higher TSH levels). When it wants your thyroid to slow down, it lets off the pedal (lower TSH levels).
- When TSH levels are too high, it indicates that your thyroid can’t produce enough T4 (hypothyroidism). It's like your body saying, "More thyroid hormone please!", but your body can't produce enough; or
- When TSH levels are too low, it indicates that your thyroid is producing too much T4 (hyperthyroidism). It's like your body saying, "No more thyroid hormone, we have enough!", but your body keeps producing an abundance of T4.
A TSH level test is the most common test for screening thyroid dysfunction, and is now recognized as being a more sensitive test than T4 for detecting hypothyroidism and hyperthyroidism [ref. 1].
Different opinions of normal thyroid function
The first questions anyone cares about when they have their TSH test results is, “is this normal?” Unfortunately, there’s no consensus on exactly what normal TSH levels are in terms of the upper limit. However:
- .45 – 5.5 mIU/L | Historically this has been the “normal” range of TSH [ref. 1, 2, 3]
- .45 – 4.5 mIU/L | In 2008 the Endocrine Society and American Medical Association adopted this range [ref. 1, 2, 3]
- < 3.0 mIU/L | The American Association of Clinical Endocrinologist now recommends this as an upper limit [ref. 3]
- < 2.5 mIU/L | National Academy of Clinical Biochemistry suggests this as an upper limit for TSH levels [ref. 4], as 95% of normal individuals have TSH levels below 2.5 [ref. 5]
These are major biological and medical organizations that have very different opinions about what normal TSH levels are. This doesn’t help you. Depending on which camp your healthcare provider falls into, he or she may say, “Everything looks normal,” whereas a different healthcare provider might tell you that you have a thyroid problem.
What are you to make of it?
Why asking “what is normal TSH?” isn’t the right question
Not only is there little consensus about what the normal limit of TSH is, but it’s definitely not the best question. The question you should be asking is:
- What are functional TSH levels?
“Normal” seems to question whether or not something is abnormal. “Functional” TSH levels addresses whether or not your thyroid is working optimally. It’s sort of like the difference between getting a “D” and an “A-.” A “D” isn’t a failing grade, but do you want it?
Along with most other functional medicine providers, we suggest that an optimal range for functional TSH levels is 1.0 – 2.0 mIU/L. This is because:
- Studies have found that TSH above 2.0 may be associated with cardiovascular risk factors [ref. 6]
- TSH between 1.0 and 2.0 has been associated with the lowest incidence of abnormal thyroid function [ref. 7]
Moreover, functional medicine aims to establish which TSH levels are going to allow you to feel the healthiest. A TSH level of 4.0 may be considered “normal” in many medical offices, but that doesn’t mean you are necessarily going to feel good. Make sense?
Have "normal" TSH levels, but still feel bad?
Now you might be asking – or you may already be in this boat – what should you do if your medical practitioner says your TSH levels are normal (such as 4.3), but you still don’t feel good? Well, you now know what suggested functional levels are, and you’re not married to your provider, so consider:
- Getting a second opinion
- Retesting TSH- TSH levels fluctuate during the day, and a retest can help establish a more accurate TSH level
- Taking other thyroid tests to help evaluate thyroid status
Remember that you know how your body is feeling better than anyone else. If something doesn’t feel right, your provider should help you get to the bottom of it.
If you are looking for more information about TSH and thyroid disease, you will probably find these comprehensive resources very informative:
What if my TSH levels are high?
For more information, see this article about TSH testing.
It’s important to note that TSH levels fluctuate throughout the day and over time, as well as in response to infections and other factors. If you TSH levels aren’t functional now, they may return to healthy levels over time. In a 2007 study published in the Archives of Internal Medicine, over 50% of patients with abnormal TSH levels on their first test had normal TSH levels when they were retested at a later date [ref. 8].
The point is, if not everything is beautiful in thyroid paradise when you first get tested, then you might wait and retest later. Of course, this is something your healthcare provider will discuss with you – if not, you might bring it up and see what they think.
You don’t marry someone after the first date. In the same way, TSH testing should never be used alone to assess your thyroid. TSH tests are helpful as a screening tool for healthy thyroid function. But further thyroid tests, such as T3 test, T4 test, Reverse T3 and don’t forget about antibody testing for a more comprehensive picture.
 Fatourechi V. Subclinical hypothyroidism: an update for primary care physicians. Mayo Clin Proc. 2009;84(1):65-71.
 Guan H, Shan Z, Teng X, et al. Influence of iodine on the reference interval of TSH and the optimal interval of TSH: results of a follow-up study in areas with different iodine intakes. Clin Endocrinol (Oxf). 2008 Jul;69(1):136-41.
 Baloch Z, Carayon P, Conte-Devolx B, et al. Laboratory medicine practice guidelines. Laboratory support for the diagnosis and monitoring of thyroid disease. Thyroid. 2003 Jan;13(1):3-126.
 Wartofsky L, Dickey RA. The evidence for a narrower thyrotropin reference range is compelling. J Clin Endocrinol Metab. 2005 Sep;90(9):5483-8.
 Benvenga S, Ruggeri RM, Russo A, Lapa D, Campenni A, Trimarchi F. Usefulness of L-carnitine, a naturally occurring peripheral antagonist of thyroid hormone action, in iatrogenic hyperthyroidism: a randomized, double-blind, placebo-controlled clinical trial. J Clin Endocrinol Metab. 2001 Aug;86(8):3579-94.
 Teng W, Shan Z, Teng X, Guan H, Li Y, Teng D, et al. Effect of iodine intake on thyroid diseases in China. N Engl J Med. 2006 Jun 29;354(26):2783-93.
 Meyerovitch J, Rotman-Pikielny P, Sherf M, et al. Serum thyrotropin measurements in the community: five-year follow-up in a large network of primary care physicians. Arch Intern Med. 2007 Jul 23;167(14):1533-8.
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