Thyroid-stimulating hormone (TSH) concentration in serum/plasma
This test measures the amount of thyroid-stimulating hormone (TSH) in your blood. TSH is a hormone produced by your pituitary gland that helps regulate your thyroid function.
["TSH helps your thyroid produce hormones that control metabolism."]
Key facts at a glance
- LOINC
- 50539-6
- Short code
- TSH sp7 SerPl-aCnc
- Synonyms
- TSH sp7 SerPl-aCnc
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 0.4
- Ref high
- 4
- Critical range
- 0.1 N/A – 20 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 84443
- SNOMED
- 301343003
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
Why This Test Is Done
Your doctor may order a TSH test to check for thyroid problems, such as hypothyroidism (when your thyroid isn’t working enough) or hyperthyroidism (when it’s working too much). It’s often the first test done to evaluate thyroid function, especially if you have symptoms like fatigue, weight changes, or unexplained issues with your heart or digestion.
What to Expect Before the Test
No special preparation is usually needed, but you may be asked to fast for 8–12 hours before the test if it’s part of a larger blood panel. Bring any medications you’re taking, as some (like certain thyroid medications) can affect results.
How the Test Works
A small sample of blood is drawn from a vein in your arm. The blood is then sent to a lab, where it’s analyzed to measure TSH levels using an immunoassay method.
What the Results Mean
Results help doctors determine whether your thyroid is functioning normally. Abnormally high or low TSH levels may indicate thyroid disorders that require further testing or treatment.
Reference range
Adult: 0.4-4.0 mIU/LN/A
Take your thyroid medication after the blood draw if applicable. No fasting required.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
TSH is a key marker for thyroid health. Low TSH often signals hyperthyroidism, while high TSH usually points to hypothyroidism. Since TSH can fluctuate slightly over time, doctors may repeat the test if initial results are borderline or if symptoms persist.
Short name
TSH Level
Frequently asked questions
What causes TSH levels to be checked?
Can diet or medications affect TSH results?
How long does it take to get TSH results?
Sources
- 1
- 2Lab Tests OnlineSource
- 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 16, 2026. · Read our editorial policy