Thyroid-stimulating hormone (TSH) with serum/plasma measurement by immunoassay
This test measures the level of thyroid-stimulating hormone in your blood, which helps your body regulate thyroid function.
["TSH helps assess whether your thyroid is working properly."]
Key facts at a glance
- LOINC
- 12927-0
- Short code
- T4 sp6 p chal SerPl-mCnc
- Synonyms
- T4 sp6 p chal SerPl-mCnc
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 4.5
- Ref high
- 12
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 84436
- SNOMED
- 302345006
- 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 check for thyroid problems, such as hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid). It’s often the first test used to diagnose these conditions because it’s sensitive and reliable. TSH levels can also be checked during pregnancy, before starting certain medications, or if you have symptoms like fatigue, weight changes, or unexplained mood swings.
What to Expect Before the Test
No special preparation is needed for this blood test. You may be asked to fast for 8–12 hours before the test if your doctor recommends it, but this is not always required. Bring any medications you’re currently taking to your appointment, as some can affect TSH levels.
What Happens During the Test?
A healthcare professional will draw blood from a vein in your arm using a small needle. You may feel a slight pinch, but it usually doesn’t cause significant discomfort. The blood sample is then sent to a lab for analysis.
What Are the Results?
Results are reported in units of picograms per milliliter (pg/mL) or international units per liter (IU/L). Your doctor will compare your results to a reference range specific to your lab and medical situation. High or low TSH levels may indicate thyroid issues that need further evaluation.
Reference range
Adult: 4.5-12.0 μg/dLN/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 levels often suggest hyperthyroidism (overactive thyroid), while high TSH levels typically indicate hypothyroidism (underactive thyroid). Since TSH is sensitive, it can detect even mild changes in thyroid function. Regular monitoring with TSH may be recommended if you have a history of thyroid disease, take thyroid medications, or experience symptoms like fatigue, weight changes, or hair loss.
Short name
TSH (Serum/Plasma)
Frequently asked questions
What causes abnormal TSH levels?
Will fasting affect my TSH test results?
Can TSH test results change over time?
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