Thyroid Stimulating Hormone (TSH) with Immunoassay Confirmation
Your blood test measures thyroid-stimulating hormone (TSH), a key hormone that helps regulate your thyroid function. This test confirms the results of an initial screening.
["This test helps assess whether your thyroid is working normally or if it may be underactive or overactive."]
Key facts at a glance
- LOINC
- 40673-6
- Short code
- TSH BII Ser-aCnc
- Synonyms
- TSH BII Ser-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 this test if you have symptoms like fatigue, weight changes, or unexplained mood swings. It’s also used to monitor thyroid conditions, such as hypothyroidism or hyperthyroidism, or to check for thyroid dysfunction before or after treatment.
What to Expect Before the Test
No special preparation is needed, but you may be asked to fast for 8–12 hours before the test if it’s part of a fasting panel. Bring any medications you’re currently taking to your appointment.
How the Test Works
A small blood sample is drawn from a vein in your arm. The blood is sent to a lab where it’s tested for TSH levels using an immunoassay method, which detects the hormone in your blood.
What the Results Mean
High or low TSH levels can indicate thyroid issues, but your doctor will interpret the results in relation to your symptoms and medical history. Results are not given as a standalone number but as a comparison to expected ranges.
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 are critical for diagnosing and managing thyroid disorders. Low TSH may suggest hyperthyroidism (overactive thyroid), while high TSH often points to hypothyroidism (underactive thyroid). Confirmatory testing ensures accurate diagnosis and guides treatment decisions, such as medication adjustments or further testing.
Short name
TSH Confirmation
Frequently asked questions
What does a high TSH level mean?
What does a low TSH level mean?
How often should I get this test?
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