Thyroid Stimulating Hormone (TSH) with Serum/Plasma Measurement by Immunoassay
This blood test measures your thyroid-stimulating hormone, a key hormone that helps regulate your metabolism and thyroid function.
["Your TSH level helps doctors check for thyroid problems."]
Key facts at a glance
- LOINC
- 12940-3
- Short code
- TSH 30M pre chal SerPl-aCnc
- Synonyms
- TSH 30M pre chal 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 Is This Test Done?
Your doctor may order a TSH test to diagnose or monitor conditions like hypothyroidism (underactive thyroid), hyperthyroidism (overactive thyroid), or thyroid cancer. It’s also used to check for pituitary gland issues that affect thyroid hormone production.
What to Expect Before the Test
No special preparation is needed, but avoid smoking or caffeine 30 minutes before the blood draw. If you’re on thyroid medication, check with your doctor first—some medications can affect TSH levels.
What the Results Mean
Higher-than-normal TSH often suggests hypothyroidism, while very low TSH may indicate hyperthyroidism or thyroid dysfunction. Your doctor will interpret results in relation to your symptoms and medical history.
Common Conditions This Test Helps Identify
This test is critical for diagnosing thyroid disorders, including Hashimoto’s disease (autoimmune hypothyroidism), Graves’ disease (hyperthyroidism), and thyroid nodules. It can also help assess pituitary dysfunction or thyroid hormone resistance.
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 levels can be influenced by stress, pregnancy, certain medications (e.g., lithium, amiodarone), and chronic illnesses like kidney disease or liver failure. Always discuss any recent changes in your health or medications with your provider.
Short name
TSH Level
Frequently asked questions
Why might my TSH test show unexpected results even if I feel fine?
Can diet affect my TSH test results?
What if my TSH is borderline? What should I do next?
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