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Thyroid Stimulating Hormone (TSH) by Immunoassay (Serum/Plasma)

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

This blood test measures your thyroid-stimulating hormone, a key hormone that regulates your thyroid function. It helps diagnose and monitor thyroid disorders like hypothyroidism or hyperthyroidism.

Quick summary

["TSH helps your doctor check if your thyroid is working properly."]

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

Key facts at a glance

LOINC
12944-5
Short code
TSH sp5 p chal SerPl-aCnc
Synonyms
TSH sp5 p 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 evaluate symptoms such as fatigue, weight changes, or unexplained mood swings. It’s also used to monitor thyroid conditions, screen for thyroid problems, or check after treatment for thyroid disorders.

What Does a TSH Test Measure?

TSH is produced by your pituitary gland and signals your thyroid to produce thyroid hormones (like thyroxine, T4). High or low TSH levels can indicate whether your thyroid is overactive or underactive.

How Is the Test Performed?

A blood sample is taken from a vein in your arm. The sample is sent to a lab where it’s analyzed using an immunoassay method to detect TSH levels.

What Are Common Results?

Results are typically reported in international units per liter (IU/L). A normal range varies slightly by lab, but low TSH often suggests hyperthyroidism, while high TSH often suggests hypothyroidism.

Reference range

Adult: 0.4-4.0 mIU/LN/A

Specimen: serum

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 a critical marker for thyroid health. Low levels may indicate overactive thyroid (hyperthyroidism), while elevated levels suggest underactive thyroid (hypothyroidism). It’s often the first test used to diagnose thyroid disorders and guide treatment decisions.

Short name

TSH

Frequently asked questions

What causes abnormal TSH levels?
Abnormal TSH levels can result from thyroid diseases (e.g., Hashimoto’s thyroiditis, Graves’ disease), pituitary disorders, thyroid surgery, radiation therapy, or certain medications (e.g., amiodarone, lithium). Stress, pregnancy, or autoimmune conditions may also affect TSH.
How long does it take to get results?
Results are usually available within 1–3 business days, depending on your lab’s processing time. Your doctor will discuss the findings with you during your follow-up visit.
Can lifestyle changes affect TSH levels?
Yes, diet (e.g., iodine intake), stress, sleep, and certain medications can influence TSH. Avoiding iodine-rich foods (like seafood) or supplements before testing may help if your doctor recommends it.
  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