Thyroid-stimulating hormone (TSH) measured by immunoassay (serum/plasma)
This test measures the level of thyroid-stimulating hormone in your blood, which helps your thyroid gland produce hormones that regulate metabolism.
["TSH helps doctors check if your thyroid is working properly."]
Key facts at a glance
- LOINC
- 50536-2
- Short code
- TSH sp4 SerPl-aCnc
- Synonyms
- TSH sp4 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 thyroid conditions, such as hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid). It’s often the first test used to check thyroid function, especially if you have symptoms like fatigue, weight changes, or unexplained mood swings.
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 more complex evaluation. Bring any medications you’re taking, as some (like certain thyroid medications) can affect results.
What the Results Mean
Results are interpreted based on your symptoms and overall health. Low TSH often suggests an underactive thyroid, while high TSH may indicate an overactive thyroid or thyroid issues like Hashimoto’s disease. Your doctor will discuss findings in the context of your medical history.
Common Conditions This Test Helps Diagnose
TSH testing is critical for diagnosing thyroid disorders, including primary hypothyroidism (e.g., Hashimoto’s thyroiditis), primary hyperthyroidism (e.g., Graves’ disease), and thyroid nodules. It can also help monitor treatment for thyroid conditions.
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.
Clinical significance: TSH is the gold standard for initial thyroid function screening. Abnormal levels can signal underlying thyroid dysfunction, prompting further testing (e.g., free T4, antibodies) or treatment adjustments. It’s especially useful in asymptomatic individuals or those with risk factors (e.g., family history, autoimmune conditions).
Short name
TSH
Frequently asked questions
What causes TSH levels to be too high?
What causes TSH levels to be too low?
Does diet affect TSH test 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