TSH Levels: Low To High Ranges, Symptoms, And What They Mean

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Medical News TodaySubscribeWhat are the ranges, symptoms, and meaning of TSH levels?

Medically reviewed by Marina Basina, MD — Written by Jamie Eske — Updated on April 22, 2025

Normal ranges
By sex
By age
In pregnancy
In children
High levels
Low levels
How to measure
Factors that affect levels
FAQ
Summary

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, 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.

What are normal TSH ranges?

An infographic guide showing the ranges of TSH levels. — MNT-infographic_guide infographic by Diego Sabogal 1401179-TSH-levels-original

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.

The following table provides estimates of TSH levels that doctors consider low (indicating hyperthyroidism), normal, and high (indicating hypothyroidism):

Hyperthyroidism	Normal	Mild hypothyroidism	Hypothyroidism
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 2016 review suggests that normal levels are more likely to fall between 0.5 to 2.5 milli-international units (mIU) per milliliter (mL).

TSH levels by sex

A note about sex and gender

Sex and gender exist on spectrums. This article will use the terms “male,” “female,” or both to refer to sex assigned at birth. Learn more.

Females are more likely to experience thyroid dysfunction than males. The Office on Women’s Health reports that 1 in 8 females experience thyroid problems at some point. This includes hyperthyroidism and hypothyroidism.

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. For example, studies in 2020 investigating Chinese and French populations suggest that TSH levels are higher in females, but other factors, such as age, are more likely to affect TSH levels.

TSH levels by age

Blood TSH levels tend to increase as people get older, with evidence suggesting that hypothyroidism is the most common thyroid condition in people over age 60 years and steadily increases with age.

Research involving older adults suggests that roughly 7 to 14% of people may have TSH levels above the upper limit of reference ranges.

Normal TSH levels in pregnancy

Pregnancy hormones naturally increase the levels of certain thyroid hormones in the blood. This is essential for the development of the fetal brain and nervous system.

At the same time, the levels of TSH in the blood decrease. The TSH target levels per trimester of pregnancy are:

First Trimester: 0.1-2.5 mU/L
Second Trimester: 0.2-3.0 mU/L
Third Trimester: 0.3-3.0 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 pregnancy-related complications, such as:

preeclampsia
premature birth
low birth weight
congestive heart failure

Normal TSH levels in children

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 4.5 to 10 mU/L.

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

What do high levels mean?

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.

Symptoms of hypothyroidism may include:

fatigue
weight gain
swelling of the face and neck
increased sensitivity to cold temperatures
dry skin
thinning hair
slow heart rate
irregular or heavy menstrual periods
fertility problems
depression
constipation

What do low levels mean?

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.

Symptoms of hyperthyroidism can include:

irregular or rapid heart rate
muscle weakness
nervousness or irritability
difficulty sleeping
frequent bowel movements or diarrhea
weight loss
mood changes

How to measure TSH levels

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 best way to monitor thyroid function. However, if a person has abnormally high or low TSH levels, the doctor may need to perform at least one other diagnostic test to identify the underlying cause. These tests look at levels of specific thyroid hormones and antibodies.

Factors that affect levels

In addition to age, sex, and pregnancy status, many other factors can affect TSH levels. Evidence suggests that genetic, environmental, or intrinsic factors can alter TSH levels. Some of these factors may include:

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

Frequently asked questions

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 when TSH levels are 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 normal TSH level in females?

Normal TSH levels, in both females and males, range from 0.4 to 4.0 milliunits per liter (mU/L).

What is a good TSH level for age?

Summary

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.

Endocrinology
Hypothyroid
Blood / Hematology
Medical Devices / Diagnostics

How we reviewed this article:

SourcesMedical News Today has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical journals and associations. We only use quality, credible sources to ensure content accuracy and integrity. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.

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Medically reviewed by Marina Basina, MD — Written by Jamie Eske — Updated on April 22, 2025

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