High thyroid-stimulating hormone (TSH) levels based on a TSH test may mean you have hypothyroidism (underactive thyroid), while low TSH levels suggest hyperthyroidism (overactive thyroid). Show
TSH values are described as follows:
But, there are exceptions to these interpretations as well as variations as to what a "normal" TSH level is. This is because TSH levels can vary by age, male and female sex, and other factors. In the end, the results need to be interpreted alongside other thyroid function tests to make the correct diagnosis. This article looks at the causes of high and low TSH levels, what they mean, and the various factors that can influence test results. What Is TSH?TSH is a hormone that acts as a messenger to the thyroid gland. When released by the pituitary gland—a small gland located at the base of the brain—TSH stimulates the thyroid to produce more thyroid hormone. A high TSH suggests your thyroid is underactive (hypothyroid) and not doing its job of producing enough thyroid hormone. A low TSH suggests your thyroid is overactive (hyperthyroid) and producing excess thyroid hormone. How TSH Levels ChangeTSH levels seem counterintuitive. Why does a high TSH mean you have an underactive thyroid gland? And why do low levels mean it's overactive? To answer that, you have to know that TSH and thyroid hormones are different things. The thyroid hormones are:
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, your pituitary makes more TSH. That signals the thyroid to increase production. When levels are high, the pituitary releases less TSH. That signals the thyroid to slow down. This is why high TSH indicates low thyroid function and vice versa. Interpreting TSH LevelsUnderstanding when and why thyroid hormone is 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 4.0 mU/L. As with most medical conditions and tests, however, there are exceptions to this rule. Verywell / Emily Roberts Controversies Over Optimal TSHMany non-modifiable factors influence a person's TSH levels and dictate what a "normal" value is in an individual. This not only includes variations by a person's biological sex or age but fluctuations that regularly occur during different seasons of the year. Some experts argue that the upper limit of a normal TSH should be lower—around 2.5 mU/L. The reasoning behind this is that the vast majority of adults without thyroid disease have a TSH value between 0.45 and 4.12 mU/L. This is especially true in younger females. Differences in TSH Levels in Females and MalesSome studies suggest that a normal TSH range in younger females may be closer to 0.4-2.5 mU/L. This is due to the fact that TSH concentrations are higher in females than in males whose normal TSH range is closer to 0.4-4.0 mU/L In addition, some healthcare providers believe that older patients should have a TSH level that is greater than 4.0 mU/L or 5.0 mU/L, since TSH normally increases with age. Many healthcare providers sidestep this controversy by simply looking at each person as an individual. For example, a person who still has significant symptoms of hypothyroidism at a TSH of 4.0 mU/L may do better with a goal TSH of around 1.0 mU/L. In contrast, someone who has health risks—such as heart disease or osteoporosis—may benefit from having a goal TSH that is higher, perhaps around 5.0 mU/L or 6.0 mU/L During pregnancy, TSH should not be allowed to rise above 2.4 mU/L in the first trimester or 3.0 mU/L in the second and third. That protects the health of both the baby and mother. Causes of High TSHA high TSH means different things depending on whether a person has known thyroid disease or not. In People Without Known Thyroid DiseaseA high TSH in people who are not undergoing thyroid disease treatment usually indicates the presence of primary hypothyroidism. This is by far the most common form of hypothyroidism, and it occurs because the thyroid gland produces an inadequate amount of thyroid hormones. The pituitary gland senses these low levels and increases the production of TSH. An elevated TSH may also occur with normal thyroid function due to the presence of antibodies, proteins made by the immune system. In People Being Treated for Thyroid DiseaseA 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 being 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. Causes of Low TSHA low TSH often means that a person has an elevated level of thyroid hormones. In People Without Known Thyroid DiseaseLow TSH is most often associated with hyperthyroidism. This can be due to a number of causes, ranging from autoimmune disease to lumps in the thyroid gland (toxic nodules) to an abnormally enlarged thyroid gland (goiter). It can also occur during a normal pregnancy as thyroid hormones are affected by "the pregnancy hormone" human chorionic gonadotropin (hCG). Less often, a lack of TSH produced by the pituitary gland (due to dysfunction) can lead to low levelsof thyroid hormone in the blood—a condition known as central hypothyroidism. This is an exception to the general rule that hypothyroidism is associated with a high TSH. Central hypothyroidism is uncommon and usually associated with a deficiency of other pituitary hormones. This deficiency leads to a number of other symptoms as well. In People With Thyroid DiseaseIn 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 to be monitored to make sure 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 Thyroid
Underactive Thyroid + Low TSH
Factors That Can Skew TSH ResultsThere are a number of factors that can affect TSH levels. These are important to consider 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 prove to be ineffective. Laboratory ErrorIf 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. AntibodiesAntibodies are thought to interfere with accurate thyroid testing in roughly 1% of people. In a 2018 review, such interference caused either misdiagnosis or inappropriate treatment in more than 50% of people who have these antibodies:
Health and HabitsA number of other factors can affect TSH test results, including:
Testing MethodA 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 EnoughDuring diagnosis, most healthcare providers use the TSH test to evaluate thyroid function and determine the optimal course of treatment. There are times, however, when knowing one's TSH may be insufficient. For instance, free T4 in addition to TSH is 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 being hyperthyroid or hypothyroid, free T4 may be checked. TSH is also not necessarily sufficient to monitor hypothyroidism during pregnancy; T4 and free T4 are often recommended. Depending on the clinical situation, other thyroid tests that may be done include (T3), free T3, reverse T3, and thyroid antibody tests. SummaryA TSH level that is optimal for all people cannot quite be established. That's because TSH levels vary depending on numerous factors, including your age, your thyroid condition, and possibly even how well you sleep at night or when you last ate. To gauge the optimal level for you, your healthcare provider should consider these factors along with any symptoms you are experiencing. You can also improve the accuracy of your tests by keeping any factors that may influence your results as consistent as possible. 5 Common Misconceptions About Thyroid DiseaseA Word From VerywellThe TSH test is the gold standard in diagnosing and monitoring thyroid disease. But as with any medical test, there are exceptions to what the test results may mean, as well as situations in which the test may be inaccurate. It is entirely possible that 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. And if you don't feel you're being heard, consider seeking a second opinion. Frequently Asked Questions
What is a normal TSH level in a woman?TSH normal values are 0.5 to 5.0 mIU/L. Pregnancy, a history of thyroid cancer, history of pituitary gland disease, and older age are some situations when TSH is optimally maintained in different range as guided by an endocrinologist.
What is normal TSH level for age?
What is a good range for thyroid stimulating hormone?Normal Values:
Normal values are from 0.4 to 4.0 mIU/L for those with no symptoms of an under- or over-active thyroid. Some people with a TSH value over 2.0 mIU/L, who have no signs or symptoms suggestive of an under-active thyroid, may develop hypothyroidism sometime in the future.
What is considered low TSH?The normal range for TSH is between 0.4 mU/L and 4.0 mU/L. 1. What does it mean when your TSH levels are low? 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.
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