Table of ContentsView AllTable of ContentsWhat Is TSH?How TSH Levels ChangeInterpreting ResultsNormal TSHCauses of High TSHCauses of Low TSHFactors Influencing ResultsValue of TSH Testing
Table of ContentsView All
View All
Table of Contents
What Is TSH?
How TSH Levels Change
Interpreting Results
Normal TSH
Causes of High TSH
Causes of Low TSH
Factors Influencing Results
Value of TSH Testing
Normal thyroid-stimulating hormone (TSH) levels generally fall between 0.4 and 4.5 milliunits per liter (mU/L).
TSHlevels higher than 4.5 mU/L usually indicate an underactive thyroid (hypothyroidism), and low TSH levels—below 0.4 mU/L—indicate an overactive thyroid (hyperthyroidism).
Verywell / Emily Roberts
What Is Thyroid-Stimulating Hormone (TSH)?
TSH levels seem counterintuitive. A high TSH suggests anunderactivethyroid gland, while low TSH levels indicate anoveractivethyroid.
TSH and thyroid hormones are different. The thyroid hormones include:
Your body uses thyroid hormones to regulate all kinds of processes. That includes how fast you burn calories, your heart rate, and many other automatic functions.
When thyroid hormones are low, the pituitary makes more TSH, which signals the thyroid to increase production. When levels are high, the pituitary releases less TSH, which signals the thyroid to slow down. This is why high TSH indicates low thyroid function and vice versa.
Interpreting TSH Levels
Understanding when and why thyroid hormones are released (or not) helps clear up what a low TSH and a high TSH level reveal about your thyroid’s function.
TSH is measured in mU/L. This abbreviation stands for milliunits per liter, with one milliunit equating to one-thousandth of a unit.
The normal range for TSH is generally between 0.4 mU/L and 4.5 mU/L.However, as with most medical conditions and tests, there are exceptions to this rule.
Some experts argue that the upper limit of a normal TSH should be lower—around 2.5 mU/L. This is because most adults without thyroid disease have a TSH value between 0.45 and 4.12 mU/L, especially in younger females.
You may still have symptoms despite a normal TSH level. If this is the case, speak up. Even a “normal” TSH may be abnormal for you.
Some studies suggest a normal TSH range in younger females aged 18 to 29 may be closer to 0.4-2.5 mU/L.The normal TSH range in males is closer to 0.4-4.0 mU/L.
Low estrogen impairs the thyroid gland’s ability to make thyroid hormones. So, TSH rises to get the thyroid to produce more. High estrogen leads to increased thyroid hormone production and lower TSH. Inmenopause, estrogen levels are lower, which sometimes triggers thyroid disease.
TSH Levels During Pregnancy
Higher TSH levels (TSH levels > 4.5 mU/L) in early pregnancy are associated with an increased risk of miscarriage.
In addition, some healthcare providers believe that older patients should have a TSH level greater than 4.0 mU/L or 5.0 mU/L since TSH typically increases with age.
In contrast, someone who has health risks—such asheart diseaseorosteoporosis—may benefit from having a higher goal TSH, perhaps around 5.0 mU/L or 6.0 mU/L
A high TSH level—above 4.5 mU/L—indicates an underactive thyroid, also known as hypothyroidism. This means your body is not producing enough thyroid hormone. A high TSH means different things depending on whether a person has known thyroid disease.
In People Without Known Thyroid Disease
A high TSH in people who are not undergoing thyroid disease treatment usually indicates the presence of primary hypothyroidism.
In People Being Treated for Thyroid Disease
A high TSH may be found in people being treated for either hypo- or hyperthyroidism.
With hypothyroidism, a high TSH usually means that the dose of thyroid hormone replacement needs to be increased.
In some cases, however, the dose is okay, but the medication is not fully absorbed. For example, many foods and medications can affect the absorption of Synthroid (levothyroxine) in your system. Learning what to avoid while taking this medication is important for it to work properly.
With hyperthyroidism, a high TSH usually means that the treatment—be it surgery, radioactive iodine, or medications—was so effective in limiting the production of thyroid hormone that it caused the person to become hypothyroid.
A low TSH often means a person has an elevated level of thyroid hormones. A low TSH level—below 0.4 mU/L—indicates an overactive thyroid, also known as hyperthyroidism. This means your body is producing an excess amount of thyroid hormone.
Central hypothyroidismis uncommon and usually associated with a deficiency of other pituitary hormones. This deficiency leads to several other symptoms as well.
In People With Thyroid Disease
In people being treated for hypothyroidism, a low TSH level may mean:
In people being treated for hyperthyroidism, a low TSH level usually means that further treatment is needed to reduce thyroid hormone levels.
It could also mean that a person must continue monitoring to ensure thyroid hormone levels return to normal. This is often the case for people who have temporary thyroiditis related to pregnancy or chemotherapy treatment.
Underactive Thyroid + High TSHTreatment may need to be more aggressiveMedication may not be absorbing enoughUnderactive Thyroid + Low TSHTreatment may be more aggressive than neededMedication may be absorbing too much
Underactive Thyroid + High TSHTreatment may need to be more aggressiveMedication may not be absorbing enough
Treatment may need to be more aggressive
Medication may not be absorbing enough
Underactive Thyroid + Low TSHTreatment may be more aggressive than neededMedication may be absorbing too much
Treatment may be more aggressive than needed
Medication may be absorbing too much
Factors That Can Skew TSH Results
A number of factors can affect TSH levels. These are important because lab values don’t tell the whole story about someone’s condition.
A treatment plan that does not also consider someone’s symptoms may be ineffective.
Laboratory Error
If a TSH test result is unexpected, simply repeating the test is often the best course of action.
Errors can occur during the blood draw, in transcribing the results, or due to mix-ups in the lab. Statistically, there is always a risk of lab error, and results should always be interpreted along with clinical symptoms and findings.
Antibodies
Antibodies can interfere with accurate thyroid testing in some people.In one review of studies, such interference caused either misdiagnosis or inappropriate treatment in more than 50% of people who have these antibodies:
Health and Habits
Several other factors can affect TSH test results, including:
Testing Method
A capillary finger prick test, or blood spot test, is a somewhat controversial alternative to traditional TSH testing.
It uses a finger prick rather than a standard blood draw from your vein to evaluate thyroid function. Blood spot testing kits have also been developed so that you can monitor your TSH level from home.
Proponents of this test believe that it ensures greater accuracy without requiring as much of a sample as a venous blood draw.
However, since the test is not widely available right now, it’s unknown exactly how well the test compares with conventional TSH testing.
When TSH Alone Is Not Enough
Most healthcare providers use the TSH test during diagnosis to evaluate thyroid function and determine the optimal course of treatment. However, knowing one’s TSH may be insufficient at times.
For instance, free T4 and TSH are usually tested if a healthcare provider suspects thyroid dysfunction due to disease of the pituitary gland or hypothalamus.
Likewise, if the TSH is normal but a person still has symptoms of hyperthyroidism or hypothyroidism, free T4 may be checked.
TSH is also not necessarily sufficient to monitor hypothyroidism during pregnancy; T4 and free T4 are often recommended.
Other thyroid tests that may be performed, depending on the clinical situation, include (T3), free T3, reverse T3, and thyroid antibody tests.
Summary
An optimal TSH level for all people cannot reasonably be established. That’s because TSH levels vary depending on numerous factors, including age, thyroid condition, and possibly even how well you sleep at night or when you last ate. Your healthcare provider will consider these factors and any symptoms you’re experiencing to determine your optimal range.
The TSH test is the gold standard in diagnosing and monitoring thyroid disease. However, as with any medical test, there are exceptions to what the test results may mean and situations in which the test may be inaccurate. Your healthcare provider may order additional tests to help determine how your thyroid gland is performing.
2:195 Common Misconceptions About Thyroid Disease
2:19
5 Common Misconceptions About Thyroid Disease
18 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
American Thyroid Association.TSH reference ranges should be used to safely guide thyroid hormone treatment in hypothyroid patients.
Kuzmenko NV, Tsyrlin VA, Pliss MG, Galagudza MM.Seasonal variations in levels of human thyroid-stimulating hormone and thyroid hormones: a meta-analysis.Chronobiol Int.2021 Mar;38(3):301-17. doi:10.1080/07420528.2020.1865394
Frank-Raue K, Raue F.Thyroid dysfunction in peri-and postmenopausal women—cumulative risks.Dtsch Arztebl Int. 2023;120(18):311-316. doi:10.3238/arztebl.m2023.0069
Samuels MH, Kolobova I, Antosik M, Niederhausen M, Purnell JQ, Schuff KG.Thyroid function variation in the normal range, energy expenditure, and body composition in l-t4–treated subjects.J Clin Endocrinol Metab. 2017;102(7):2533-2542. doi:10.1210/jc.2017-00224
Park CE.Evaluation of pregnancy and thyroid function.Korean J Clin Lab Sci.2018;50:1-10. doi:10.15324/kjcls.2018.50.1.1
American Thyroid Association.Thyroid and pregnancy: Thyroid status and risk of miscarriage.
Chaker L.Hypothyroidism.Lancet. 2017 Sep;390(10101):1550-1562. doi:10.1016/S0140-6736(17)30703-1
Mcmillan M, Rotenberg KS, Vora K, et al.Comorbidities, concomitant medications, and diet as factors affecting levothyroxine therapy: results of the CONTROL Surveillance Project.Drugs in R&D. 2016 Mar;16(1):53-68. doi:10.1007/s40268-015-0116-6
De Leo S.Hyperthyroidism.Lancet. 2016 Aug;388(10047):906-918. doi:10.1016/S0140-6736(16)00278-6.
Ross DS.2016 American Thyroid Association guidelines for diagnosis and management of hyperthyroidism and other causes of thyrotoxicosis.Thyroid. 2016 Oct;26(10):1343-1421. doi:10.1089/thy.2016.0229
Cheng X, Guo X, Chai X, Hu Y, Lian X, Zhang G.Heterophilic antibody interference with TSH measurement on different immunoassay platforms.Clin Chim Acta. 2021;512:63-65. doi:10.1016/j.cca.2020.11.018
Favresse J, Burlacu MC, Maiter D, Gruson D.Interferences with thyroid function immunoassays: Clinical implications and detection algorithm.Endocrine Rev. 2018 Jul;39(5):830-850. doi:10.1210/er.2018-00119
Nair R, Mahadevan S, Muralidharan RS, Madhavan S.Does fasting or postprandial state affect thyroid function testing?Indian J Endocrinol Metab. 2014 Sep;18(5):705-707. doi:10.4103/2230-8210.139237
National Institute of Diabetes and Digestive and Kidney Diseases.Thyroid tests.
Ardabilygazir A, Afshariyamchlou S, Mir D, Sachmechi I.Effect of high-dose biotin on thyroid function tests: Case report and literature review.Cureus. 2018 Jun;10(6):e2845. doi:10.7759/cureus.2845
Song L, Lei J, Jiang K, et al.The association between subclinical hypothyroidism and sleep quality: A population-based study.Risk Manag Healthc Policy. 2019 Dec;12(1):369-374. doi:10.2147/RMHP.S234552
Sheehan MT.Biochemical testing of the thyroid: TSH is the best and, oftentimes, only test needed - A review for primary care.Clin Med Res. 2016 May;14(2):83-92. doi:10.3121/cmr.2016.1309
Meet Our Medical Expert Board
Share Feedback
Was this page helpful?Thanks for your feedback!What is your feedback?OtherHelpfulReport an ErrorSubmit
Was this page helpful?
Thanks for your feedback!
What is your feedback?OtherHelpfulReport an ErrorSubmit
What is your feedback?
By clicking “Accept All Cookies”, you agree to the storing of cookies on your device to enhance site navigation, analyze site usage, and assist in our marketing efforts.Cookies SettingsAccept All Cookies
By clicking “Accept All Cookies”, you agree to the storing of cookies on your device to enhance site navigation, analyze site usage, and assist in our marketing efforts.
Cookies SettingsAccept All Cookies
