The thyroid-stimulating hormone (TSH) test measures the amount of TSH in the blood to convey how well a person’s thyroid functions. Typically, normal levels are 0.4–4.0 milliunits per liter (mU/l)
Doctors can use TSH test results to diagnose thyroid disorders, such as hypothyroidism and hyperthyroidism.
The pituitary gland produces TSH, which is a hormone that stimulates the thyroid gland. The thyroid is a butterfly-shaped gland in the throat. It produces hormones that help regulate many bodily functions, such as metabolism, heart rate, and body temperature.
This article describes the TSH test and results. We also discuss what high and low TSH levels indicate and available treatments.
The normal range depends on a person’s age and whether they are pregnant.
The ranges tend to increase as a person gets older. Research has not shown a consistent difference in TSH levels between males and females.
However, according to the American Thyroid Association, doctors generally consider levels are within a normal range between 0.4–4.0 milliunits per liter (mU/l).
The following table provides estimates of TSH levels that are normal, low (indicating hyperthyroidism), and high (indicating hypothyroidism):
| Hyperthyroidism | Normal | Mild hypothyroidism | Hypothyroidism |
| 0–0.4 | 0.4–4 | 4–10 | 10 |
Many labs use these reference values.
However, there is some debate about these ranges. The author of a
Females are more likely to experience thyroid dysfunction than males. The
Research does not show a consistent difference in TSH levels between males and females. However, some evidence suggests that TSH levels are generally higher in females. For example, studies in 2020 investigating Chinese and
In some people, thyroid conditions are linked with sexual dysfunction. This may affect more males than females. According to a 2019 study, 59–63% of males with hypothyroidism also experience sexual dysfunction, compared with 22–46% of females who have hypothyroidism.
Blood TSH levels tend to increase as people get older, with evidence noting that hypothyroidism is the most common thyroid condition in people over 60 and steadily increases with age.
Research involving older adults suggests that roughly
Pregnancy hormones
At the same time, the levels of TSH in the blood decrease. As a result, doctors use lower reference ranges during pregnancy. The lower TSH range is decreased by around 0.4 mU/l, and the upper limit reduced by approximately 0.5 mU/l.
Levels of TSH in the blood increase gradually during the second and third trimesters, but they remain lower than normal levels in women who are not pregnant.
Doctors carefully monitor TSH levels throughout pregnancy. Having unusually high or low levels can affect the risk of miscarriage and cause
- preeclampsia
- premature birth
- low birth weight
- congestive heart failure
TSH levels are highest at birth and gradually decrease as a child gets older. As such, TSH levels can vary among children. After the newborn phase, health experts may define mild hypothyroidism in children as TSH levels ranging between
The following table shows TSH levels for children by age, according to an older study using data from 512 healthy children:
| Age | Reference ranges (mU/l) |
| Day of birth | 3.84–11.75 |
| 1 month | 1.18–3.57 |
| 1 year | 1.17–3.55 |
| 5 years | 1.15–3.47 |
| 12 years | 1.09–3.31 |
| 18 years | 1.05–3.16 |
High TSH levels indicate hypothyroidism. People develop hypothyroidism when their thyroid produces low levels of hormones.
When someone’s thyroid gland does not produce enough hormones, the pituitary gland produces more TSH to compensate.
- fatigue
- weight gain
- swelling of the face and neck
- increased sensitivity to cold temperatures
- dry skin
- thinning hair
- a slow heart rate
- irregular or heavy menstrual periods
- fertility problems
- depression
- constipation
Low TSH levels indicate hyperthyroidism. This is also known as an overactive thyroid.
If a person’s thyroid gland is secreting levels of hormones that are too high, the pituitary gland produces less TSH.
- irregular or rapid heartbeat
- muscle weakness
- nervousness or irritability
- difficulty sleeping
- frequent bowel movements or diarrhea
- weight loss
- mood changes
The TSH test involves a healthcare professional drawing blood from a vein in the inner arm. They then send the blood sample for laboratory testing.
Usually, people do not need to prepare for a TSH test. However, if the doctor is checking the blood for more than one issue, a person may need to fast or prepare in another way. The doctor will provide this information beforehand.
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In addition to age, sex, and pregnancy, many other factors can also affect TSH levels.
- other conditions occurring at the same time
- medications
- supplements
- ethnicity
- diet and iodine status
- time of day and time of year
- autoantibodies and heterophilic antibodies
- smoking
- pollutants
Doctors can treat hypothyroidism with medications, such as levothyroxine, that replace the missing thyroid hormones.
A person should take this medication once a day or as prescribed. The doctor will monitor how well the treatment is working by running additional blood tests every few months.
According to the Food and Drug Administration (FDA), people should take levothyroxine once a day: in the morning and on an empty stomach, at least half an hour before eating.
The FDA also recommends that a person informs their doctor if they eat soybean flour, walnuts, dietary fiber, or cottonseed meal — these foods can affect how the body processes levothyroxine. Drinking grapefruit juice may also delay the absorption of levothyroxine.
Hyperthyroidism treatments focus on reducing thyroid hormone levels to prevent long-term health complications.
A person may need to take beta-blockers and antithyroid medications.
Another effective treatment is radioiodine therapy. This involves taking a capsule or liquid that contains radioactive iodine-131, which destroys cells that produce thyroid hormones. However, people who take radioiodine therapy may develop hypothyroidism in the future.
Surgical removal of the thyroid gland can treat severe hyperthyroidism. Doctors often reserve this for individuals who cannot take first-line medications and severe cases of hyperthyroidism.
Below are frequently asked questions regarding TSH levels
What levels of TSH are concerning?
TSH levels below 0.4mU/l indicate hyperthyroidism, while levels about 4.0mU/l indicate hypothyroidism. The further the result from these levels, the more severe the result is.
What happens if TSH is high?
High TSH levels indicate that a person has an underactive thyroid, meaning it is not producing enough essential hormones. Symptoms of hypothyroidism include fatigue, weight gain, and thinning hair.
What is a good TSH level for age?
TSH levels are very high in the first few months of life before settling into a moderate range. For adults, TSH levels tend to increase gradually in later adulthood as thyroid function slows. Despite these natural changes, 0.4–4.0 mU/l remains a static healthy range throughout life.
A TSH test measures the amount of the hormone in the blood. Doctors can use the results to diagnose thyroid conditions, such as hypothyroidism and hyperthyroidism.
Normal TSH ranges can vary widely, depending on a person’s age, sex, and weight. Reference TSH ranges remain controversial, but for most people, the normal range falls between 0.4 and 4.0 mU/l.
Having an overactive or underactive thyroid can cause health issues that interfere with a person’s daily life. During pregnancy, unusually high or low TSH levels can lead to complications.
A doctor can provide more information about the TSH test and interpret the results.