Normal thyroid-stimulating hormone (TSH) levels typically fall between 0.4 and 4.0 milliunits per liter (mU/L), according to the American Thyroid Association (ATA).
Higher levels suggest hypothyroidism, or an underactive thyroid, while lower levels indicate hyperthyroidism, or an overactive thyroid. When TSH and thyroid hormones are out of balance, this can cause a range of issues relating to the muscles, breathing, body temperature, and more.
In this article, we describe the TSH test in detail. We also explain what the results may indicate.
A TSH level test involves taking a blood sample.
A TSH blood test is similar to other simple blood tests.
A healthcare professional will usually draw blood from a vein on the inside of the elbow.
They will begin by cleaning the skin and may then place an elastic band around the upper arm to make the vein easier to access.
They will insert a needle into the vein, allowing blood to flow into the connecting tube and vial.
Once the vial contains enough blood to carry out the test, the healthcare professional will remove the needle and elastic band and place cotton wool or a bandage over the puncture site.
After labeling the blood sample, they will send it to a laboratory for testing.
What to expect
The procedure is quick, straightforward, and relatively painless.
People may feel a slight pinch when the needle first enters the skin. There may also be some minor bleeding following the removal of the needle.
Side effects are uncommon. When they do occur, they are usually mild and may include dizziness or nausea and slight skin bruising for a couple of days after the procedure.
No preparation is necessary for a standard TSH test.
However, some people may be having other types of blood test at the same time, some of which may require overnight fasting or other preparations.
People using specific medications may need to stop taking them for a time before the TSH test because some drugs can affect the results.
A doctor can provide more information on how to prepare for the TSH test.
Why is the TSH test done?
A TSH test helps doctors determine how well the thyroid gland is functioning. People may require TSH testing for several different reasons, which we explore in more detail below.
Symptoms of a thyroid problem
Symptoms of a thyroid problem can include fatigue and irritability.
The TSH test helps doctors diagnose common thyroid disorders, such as hyperthyroidism and hypothyroidism.
The signs and symptoms of hyperthyroidism, in which the thyroid overproduces hormones, include:
- anxiety or irritability
- bulging eyes
- increased appetite
- increased sensitivity to heat
- menstrual changes
- muscle weakness
- rapid or irregular heart rate
- sleep problems
- increased sweating
- thinning skin or hair
- weight loss with no apparent cause
- goiter, which is an abnormally enlarged thyroid gland
People with hypothyroidism, where the thyroid does not produce enough hormones, may experience signs and symptoms that include:
- aches and pains
- depression and memory problems
- dry skin
- high cholesterol
- low heart rate
- menstrual changes
- muscle weakness
- sensitivity to cold temperatures
- thinning hair
- weight gain
A TSH test may also help indicate other types of thyroid problem, such as:
- Graves' disease, which causes greater activity of the thyroid
- Hashimoto's disease, an autoimmune condition where the body attacks the thyroid
- thyroid nodules, which are lumps on the thyroid that contribute to an overactive thyroid
- inflammation of the thyroid gland, called thyroiditis
- postpartum thyroiditis, which is temporary thyroiditis following pregnancy
Already have a thyroid disorder diagnosis
People who have a known thyroid disorder may have regular TSH testing to monitor their condition and the effectiveness of their treatment.
Some doctors will recommend that pregnant women have TSH tests to check their thyroid hormone levels.
According to the ATA, many experts support testing for thyroid disease in women who are pregnant or thinking of becoming pregnant.
Newborn babies in the United States will also often get a routine TSH test for congenital hypothyroidism as part of their screening program.
Normal TSH ranges vary depending on several factors, including the testing laboratory.
People who are unsure what their results mean should speak to their doctor.
If a person's results show them to have high or low levels of TSH, they will usually require further testing to determine the underlying issue.
High TSH levels
Pregnancy can cause high TSH levels.
High TSH levels suggest an underactive thyroid.
However, pregnancy and Hashimoto's disease might also cause an abnormally high TSH reading.
Treatment for hypothyroidism involves taking medication daily to return hormone levels to normal.
It can sometimes take a while to determine the best dosage of medication.
Regular TSH testing can help ensure that people are getting the correct dosage to manage their specific condition.
Low TSH levels
TSH levels that are lower than normal may indicate:
- Graves' disease
- taking too much iodine or thyroid medication
Certain medications, such as steroids or dopamine, can also cause a low reading.
Treatment options for an overactive thyroid include:
- oral radioactive iodine to shrink the thyroid gland
- antithyroid medications to stop excess hormone production
- beta-blockers to alleviate some hyperthyroidism symptoms
- surgery to remove most of the thyroid gland
Doctors use a TSH blood test to help diagnose thyroid disorders. An abnormal result typically requires further investigation to determine the exact issue.
Thyroid problems are usually easy to manage with medications, surgery, or a combination of both treatments. People who have a thyroid disorder are likely to require regular TSH testing to ensure that their symptoms remain under control.