TSH Test

The TSH test measures the TSH blood level. TSH, or thyroid-stimulating hormone, is an important screening marker for thyroid disease.

More information:

  • Test Type: Blood

  • Test Results: Typically 4 days

  • Download a sample results report

Related Tests:
  • T3 Total Test
  • T4 Total Test
  • TPO Test

TSH Blood Test - More Information

The TSH test, also known as a TSH lab test, TSH level test and thyroid-stimulating hormone test, measures the TSH blood level. People who might need a TSH test can order this test online through Accesa Labs, get tested at a local lab, and get results electronically, typically in 4 business days or less.

Who Should Get a TSH Test?

The TSH test is ordered by a wide range of people who want to assess thyroid function for health maintenance, symptom evaluation, or medication monitoring. Common reasons people order this test include:

People with symptoms of hypothyroidism (underactive thyroid). Common symptoms of underactive thyroid function include fatigue, unexplained weight gain, cold intolerance, constipation, dry skin or hair, hair loss, depression, brain fog, and a slow heart rate. If one or more of these symptoms are present, a TSH test is the standard first-line screening test for hypothyroidism.

People with symptoms of hyperthyroidism (overactive thyroid). Common symptoms of overactive thyroid function include unexplained weight loss, a rapid or irregular heartbeat, anxiety, tremors, heat intolerance, increased sweating, frequent bowel movements, and difficulty sleeping. A low TSH result is the most sensitive initial indicator of hyperthyroidism.

People monitoring thyroid medication. Patients taking levothyroxine (Synthroid, Tirosint), liothyronine, or other thyroid medications need periodic TSH monitoring to ensure that their dose is correctly calibrated. TSH is typically rechecked 6–8 weeks after any dose change and at least annually once a stable dose is established.

Women who are pregnant or planning pregnancy. TSH screening is recommended for women with known thyroid disease or risk factors before and during pregnancy. TSH ranges are typically tighter during pregnancy and many women with previously normal thyroid function may develop hypothyroidism during pregnancy.

People with a family history of thyroid disease. Thyroid disorders - particularly autoimmune thyroid diseases such as Hashimoto's thyroiditis and Graves' disease - have a strong familial component. People with a first-degree relative with thyroid disease have an elevated risk of a thyroid disorder and may benefit from periodic thyroid screening.

People being evaluated for infertility or menstrual irregularities. Thyroid dysfunction is a common and treatable cause of menstrual irregularities and infertility in women. TSH testing is a standard part of fertility workup and infertility evaluation.

General thyroid health screening. Many people order a TSH test as part of a general health checkup, particularly after age 35 when thyroid dysfunction becomes more prevalent.

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How Does TSH Work?

TSH, or thyroid-stimulating hormone, is a hormone produced by the pituitary gland. Made by special cells called thyrotrope cells in the anterior part of the pituitary, TSH plays a vital role in regulating the activity of the thyroid gland. To do so, TSH binds to receptors found on the thyroid gland's follicular cells.

Regulating the thyroid gland is important because the thyroid produces several hormones which can stimulate or shut down metabolic processes in the body. The most important hormones produced by the thyroid are T3, or triiodothyronine, and T4, or thyroxine, and stimulation by TSH can turn on or off their production. This is why measuring T3 levels through the total T3 test and T4 levels through the total T4 test is sometimes done in conjunction with TSH testing.

TSH is produced by the pituitary in response to signals from the body. The body has intricate feedback mechanisms to alert the pituitary when the body needs more or less thyroid hormone to fuel metabolic processes. When the pituitary gets a signal that the body needs more thyroid activity, it releases more TSH to tell the thyroid gland to produce more thyroid hormone. If the pituitary gets a signal that the body needs less thyroid activity, it decreases its production of TSH to tell the thyroid gland to slow down its thyroid hormone production. To ensure tight, timely regulation of the thyroid gland, circulating TSH in the blood is broken down quickly by the body.

For TSH to activate the thyroid, the thyroid gland needs to be working properly. The thyroid receptors on the gland must be able to interact with circulating thyroid-stimulating hormone and enough receptors need to be available for TSH to bind to them. Signals from the thyroid receptors to the thyroid hormone production processes must be transmitted properly. The thyroid hormone production machinery needs to be able to respond to signals to produce adequate amounts of T3 and T4 once they are told to do so.

This understanding of how the thyroid gland works is helpful in making sense of what an abnormal TSH level means. When the TSH blood level is high, this suggests that the pituitary is trying to stimulate the thyroid gland. This frequently happens because the pituitary gland is getting a signal that the body needs more thyroid hormone for various processes. Clinically, a high TSH level often suggests that one has an underactive thyroid (i.e. low thyroid activity or hypothyroidism). In settings where hypothyroidism is a concern, TSH testing is often done with other lab tests as part of the more comprehensive hypothyroidism test panel.

Conversely, a low TSH level suggests that the thyroid might be overactive (i.e. high thyroid activity or hyperthyroidism). In this situation, the pituitary gland is receiving feedback from the body that the thyroid is too active and, as a result, needs less stimulation. To reduce thyroid stimulation, the pituitary gland cuts back on the production of TSH with the intention of reducing the production of thyroid hormone by the thyroid gland. While a TSH test result can help screen for an overactive thyroid, more detailed investigation of high thyroid gland activity can be done with the hyperthyroidism test panel.

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Getting a TSH Test

Getting a TSH test near you should be relatively straightforward as the TSH blood test is a common lab test and every standard Quest Diagnostics lab location should have the equipment needed to perform it. On the day of your test, a small amount of your blood will be drawn into a vial and the specimen will be run in a machine. TSH lab results come back relatively quickly and a reference range will be provided on the lab report against which you can compare your results. On the TSH sample lab report provided above, the TSH test result reported is 0.03 mIU/L which is considered low when compared against the provided normal range of 0.40-4.50 mIU/L. Low TSH levels in this case might indicated hyperthyroidism and should be interpreted in the context of clinical symptoms and possibly with more advanced thyroid lab tests.

TSH Testing - Results Interpretation

The standard reference range for TSH in non-pregnant adults is approximately 0.40–4.50 mIU/L, though ranges vary slightly by laboratory methodology. The following table summarizes how TSH results are generally interpreted:

TSH Level* Interpretation Explanation
<0.40 mIU/L Low Possible hyperthyroidism
0.40 - 4.50 mIU/L Normal Within range
4.51-10.0 mIU/L Mildly elevated Possible hypothyroidism
>10.0 mIU/L Significantly elevated Consistent with hypothyroidism

*Adapted from the American Thyroid Association guidelines

Note that TSH values must always be interpreted in the context of clinical symptoms and, when abnormal, typically alongside additional thyroid tests such as free T4 and free T3.

As a result, the measured level of TSH using the TSH blood test is useful because it serves as an indicator as to whether the thyroid gland is doing its job. Because it gives a snapshot of the overall health of the thyroid gland, the TSH test is frequently used as an initial screening test for overall thyroid health. Normally, TSH levels will vary throughout the day as the body turns on and off processes in connections with its daily cycles. As with most lab tests, measuring one's TSH levels over time is helpful because it can help identify abnormal trends that are specific to one's body.

Getting a TSH Test with Accesa Labs

Getting a TSH test is a straightforward process with Accesa Labs:

  • Order your TSH test online. Add the TSH test to your cart and submit your information.
  • Get tested at a lab near you. Get your blood drawn at the lab you selected. Appointments can be scheduled in advance to save time.
  • Download your results when available. You will be notified when you TSH test results are ready and can view or download them at your convenience. Results are typically available in 4 days or less.

No health insurance or subscription is necessary. Get started today.

Related Tests:
  • T3 Total Test
  • T4 Total Test
  • TPO Test
What is a TSH blood test?
The TSH blood test measures the level of thyroid-stimulating hormone (TSH) in the blood. TSH is produced by the pituitary gland and regulates the activity of the thyroid gland and signals it to produce more or less thyroid hormone (T3 and T4) as needed by the body. A TSH result outside of the normal range is the most sensitive initial indicator of thyroid dysfunction.
What does a low TSH level mean?
A low TSH level typically indicates that the pituitary gland is reducing its stimulation of the thyroid gland. This often occurs because the thyroid is already producing too much hormone and is consistent with hyperthyroidism (an overactive thyroid). Common causes include Graves' disease, toxic thyroid nodules, or excessive thyroid hormone replacement. A low TSH may also indicate that levothyroxine or other thyroid medication is dosed too high. Additional testing such as free T3, free T4, and thyroid antibodies can help clarify the cause.
What does a high TSH level mean?
A high TSH level typically indicates that the pituitary gland is working harder than usual to stimulate the thyroid gland. This is often in a response to insufficient thyroid hormone production and is consistent with hypothyroidism (an underactive thyroid). Common causes include Hashimoto's thyroiditis (an autoimmune condition), prior thyroid treatment, iodine deficiency, or certain medications. A single elevated TSH should be confirmed with repeat testing and evaluated alongside free T4 and, if appropriate, TPO antibody testing.
Can I use the TSH test to monitor my thyroid medication?
Yes. The TSH test is the primary tool for monitoring thyroid hormone replacement therapy. Patients taking levothyroxine or other thyroid medications should have their TSH rechecked approximately 6-8 weeks after any dose change to assess response. Once a stable dose is established, most patients require annual TSH monitoring. Patients whose TSH is outside the therapeutic range despite treatment may need dose adjustment and should discuss their results with their medical provider.
What time of day should I get my TSH tested?
TSH levels naturally fluctuate throughout the day, with the highest levels occurring in the early morning hours and the lowest in the afternoon. Morning testing is recommended for the most consistent and reproducible results - particularly when monitoring thyroid medication over time. Testing at the same time of day for follow-up tests helps ensure results are comparable across draws.
Should I get a TSH test if I'm trying to get pregnant?
Thyroid function testing is commonly recommended as part of a pre-conception health evaluation, particularly for women with a personal or family history of thyroid disease. Unrecognized or untreated hypothyroidism can affect fertility and early pregnancy outcomes. A TSH result allows a provider to identify and treat thyroid dysfunction before conception when possible.
What type of specimen will I submit?
This TSH Test is a blood test.
Do I need to fast to take this test?
Fasting is not necessary.
How long does it take to get test results?
It typically takes 4 business days or less.
Any other test codes/names?

Test Code(s): 899

Other Test Name(s): TSH

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