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Thyroid-Stimulating Hormone (TSH), Serum

Published: August 9, 2026Updated: August 16, 2026

Measures thyroid-stimulating hormone in blood to help assess thyroid gland function and the pituitary-thyroid hormone pathway.

Quick summary

["An abnormal TSH result can help determine whether the thyroid gland is overactive or underactive."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
54077-3
Short code
NB pnl Thyroid SI DBS
Synonyms
NB pnl Thyroid SI DBS
Category
thyroid
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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

What is this test?

Thyroid-stimulating hormone, or TSH, is made by the pituitary gland and signals the thyroid to produce thyroid hormones. This blood test measures TSH to help evaluate how the thyroid and pituitary are working together.

Why might I need this test?

A clinician may order TSH to investigate symptoms of an underactive or overactive thyroid, monitor thyroid treatment, or assess thyroid function during pregnancy. It is often used with a thyroid hormone test such as free T4.

How is the test performed?

A blood sample is collected, usually by drawing blood from a vein. The laboratory measures the TSH concentration in the serum, commonly using an immunoassay.

How do I prepare for the test?

Fasting is usually not required unless your clinician requests it. Tell the healthcare provider and laboratory if you take biotin supplements or thyroid medicines, because these can affect some test results.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

TSH

Frequently asked questions

Does this test diagnose a thyroid disorder by itself?
No. TSH is often interpreted together with a thyroid hormone measurement, such as free T4, and with the patient's symptoms and medical history.
Do I need to stop taking thyroid medication before the test?
Do not stop or change medication unless your clinician instructs you to do so. The timing of the blood draw may be important when monitoring thyroid treatment.
Can biotin supplements affect the result?
Some TSH immunoassays can be affected by biotin supplements. Inform the laboratory about biotin use so the result can be interpreted appropriately.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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