The thyroid-stimulating hormone (TSH) test measures the amount of TSH in the blood to convey how well a person’s thyroid functions. Normal levels are typically 0.4 to 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 its 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 the normal range to be 0.4 to 4.0 mU/L.
|0 to 0.4 mU/L||0.4 to 4 mU/L||4–10 mU/L||10 mU/L|
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
The risk of thyroid problems increases during pregnancy and around menopause.
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.
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.
Research involving older adults suggests that roughly
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 decreases by around 0.4 mU/L, and the upper limit is approximately 0.5 mU/L lower.
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
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 from
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 to 11.75|
|1 month||1.18 to 3.57|
|1 year||1.17 to 3.55|
|5 years||1.15 to 3.47|
|12 years||1.09 to 3.31|
|18 years||1.05 to 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.
Most of the time, low TSH levels indicate hyperthyroidism. This is also known as an overactive thyroid. Much more rarely, low TSH can be due to a problem with the pituitary gland.
If a person’s thyroid gland is secreting levels of hormones that are too high, the pituitary gland produces less TSH.
- irregular or rapid heart rate
- 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.
A TSH test is often the
In addition to age, sex, and pregnancy status, many other factors can affect TSH levels.
- other conditions occurring at the same time
- diet and iodine status
- time of day and time of year
- autoantibodies and heterophilic antibodies
Doctors can treat hypothyroidism with medications, such as levothyroxine, that replace the missing thyroid hormones.
A person should take this medication once per 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 per day in the morning, on an empty stomach, and at least half an hour before eating.
The FDA also recommends that a person inform 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 help 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 of about 4.0mU/L and above 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 rise abruptly to 60–80 mU/L within 30–60 minutes after delivery in healthy-term babies. This increase relates to exposing the infant to a colder environment and clamping of the umbilical cord.
The serum TSH concentration then decreases rapidly to approximately 20 mU/L about 24 hours after delivery and then more slowly to 6–10 mU/L at 1 week.
For adults, TSH levels tend to increase gradually in later adulthood as thyroid function slows. Despite these natural changes, 0.4 to 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.