2. A blood test that measures the amount of thyroid-stimulating hormone (TSH) in your blood to check how well your thyroid gland is working. TSH is made by the pituitary gland and helps control the production of thyroid hormones that regulate your metabolism, energy levels, and many other body functions. Your healthcare provider may order this test to screen for thyroid disorders, monitor your thyroid medication dosage, or investigate symptoms such as fatigue, weight changes, mood changes, or sensitivity to hot and cold temperatures.
A blood test that measures the amount of thyroid-stimulating hormone (TSH) in your blood to check how well your thyroid gland is working. TSH is made by the pituitary gland and helps control the production of thyroid hormones that regulate your metabolism, energy levels, and many other body functions. Your healthcare provider may order this test to screen for thyroid disorders, monitor your thyroid medication dosage, or investigate symptoms such as fatigue, weight changes, mood changes, or sensitivity to hot and cold temperatures.
{"TSH is produced by the pituitary gland to control thyroid hormone production","Abnormal TSH levels may indicate thyroid disorders such as hypothyroidism or hyperthyroidism","The test requires a simple blood draw, usually done in the morning","Results are measured in mIU/L (milli-international units per liter)","Normal range typically falls between 0.4-4.0 mIU/L, but may vary by laboratory"}
Key facts at a glance
- LOINC
- 3019-0
- Short code
- TSH
- Synonyms
- —
- Category
- thyroid
- Sample
- serum
- Container
- Serum Separator Tube (SST/Gold Top)
- Units
- mIU/L
- Ref low
- 0.4
- Ref high
- 4
- Critical range
- 0.01 mIU/L – 100 mIU/L
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- ≥ 0 years
- Method
- chemiluminescent-immunoassay
- CPT
- 84443
- SNOMED
- 365906006
- Specimen volume
- 1 mL minimum, 3.5 mL preferred
- Stability
- Room temperature: 24 hours, Refrigerated (2-8°C): 7 days, Frozen (-20°C or below): 30 days
- Hemolysis max
- 50
- Lipemia max
- 300
- Icterus max
- 20
- TAT
- 1–4 hours
What is this test?
The TSH (Thyroid-Stimulating Hormone) test measures the amount of TSH in your blood. TSH is a hormone produced by the pituitary gland, a small pea-sized gland located at the base of your brain. Its primary function is to regulate the production of thyroid hormones (T3 and T4) by your thyroid gland, which is located in the front of your neck.
Why is this test performed?
The TSH test is one of the most common tests used to evaluate thyroid function. Healthcare providers order this test to: screen for thyroid disorders, monitor thyroid medication dosage, investigate symptoms of thyroid dysfunction such as fatigue, weight changes, mood changes, or temperature sensitivity, and evaluate pituitary gland function.
How is the test performed?
A healthcare professional will draw a small sample of blood from a vein in your arm using a needle. The sample is then sent to a laboratory for analysis. The test typically requires no special preparation, though your doctor may advise you to stop taking certain medications temporarily. It is often recommended to have the test done in the morning, as TSH levels can fluctuate throughout the day.
Understanding your results
TSH results are measured in mIU/L (milli-international units per liter). While normal ranges typically fall between 0.4-4.0 mIU/L, it's important to note that reference ranges may vary slightly between laboratories. High TSH levels usually indicate an underactive thyroid (hypothyroidism), while low TSH levels may suggest an overactive thyroid (hyperthyroidism). Your healthcare provider will interpret your results in context with your symptoms and other test results.
Reference range
Adult reference range: 0.4 - 4.0 mIU/L. Newborns (1-3 days): 1.0 - 39.0 mIU/L. Pediatric ranges vary by age. Reference range may vary slightly between laboratories based on methodology and population.mIU/L
No fasting required. Patient should inform laboratory of current medications, especially thyroid medications, biotin supplements, or drugs affecting thyroid function. Recent radiocontrast media may interfere.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
The TSH test is crucial for diagnosing and monitoring thyroid disorders. Elevated TSH levels typically indicate hypothyroidism (underactive thyroid), where the thyroid gland does not produce enough thyroid hormones. Common causes include Hashimoto's thyroiditis, thyroid surgery, or radiation therapy. Symptoms may include fatigue, weight gain, cold intolerance, and depression. Conversely, low TSH levels suggest hyperthyroidism (overactive thyroid), which may be caused by Graves' disease, toxic nodules, or thyroiditis. Symptoms often include weight loss, rapid heartbeat, anxiety, and heat intolerance. The TSH test is also used to monitor thyroid hormone replacement therapy and to screen newborns for congenital hypothyroidism.
Short name
TSH
Part of panels
Frequently asked questions
Do I need to fast before the TSH test?
What do high TSH levels mean?
What do low TSH levels mean?
How often should I have my TSH checked?
Can medications affect my TSH results?
Sources
- 1MedlinePlus - TSH TestSource
- 2
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 10, 2026. · Read our editorial policy