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Thyroid Stimulating Hormone (TSH) with Serum/Plasma Measurement

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

This test measures the amount of thyroid-stimulating hormone (TSH) in your blood. TSH helps regulate your thyroid gland’s production of hormones that control metabolism.

Quick summary

["TSH helps doctors check for thyroid problems, including underactive or overactive thyroid."]

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

Key facts at a glance

LOINC
57854-2
Short code
TSH 5M p chal SerPl-aCnc
Synonyms
TSH 5M 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 This Test Is Done

Your doctor may order a TSH test to diagnose or monitor conditions like hypothyroidism (low thyroid hormone), hyperthyroidism (high thyroid hormone), or thyroid nodules. It’s often the first test for thyroid issues because it’s sensitive and easy to measure.

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 your blood is drawn early in the morning. Wear comfortable clothing for easy access to your arm.

How the Test Works

A healthcare provider will draw blood from a vein in your arm. The blood sample is sent to a lab, where it’s tested for TSH levels using an immunoassay method to detect the hormone.

What the Results Mean

Results are reported in international units per liter (IU/L). High TSH levels often indicate an underactive thyroid, while low levels may suggest an overactive thyroid or other conditions. Your doctor will interpret results in relation to your symptoms and other tests.

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.

◆Associated findings1

Short name

TSH Level

Frequently asked questions

What does a TSH test help diagnose?
A TSH test is commonly used to screen for thyroid disorders, such as hypothyroidism (e.g., Hashimoto’s disease) or hyperthyroidism (e.g., Graves’ disease). It can also help monitor thyroid function after treatment for thyroid conditions or during pregnancy.
How often should I get a TSH test?
Your doctor will determine how often you need a TSH test based on your health status, symptoms, and treatment plan. Regular monitoring may be recommended if you have a history of thyroid issues or take thyroid medication.
Can lifestyle changes affect TSH results?
Yes, certain factors like stress, sleep disturbances, or medications (e.g., lithium, amiodarone) can influence TSH levels. Avoiding these factors before testing can help ensure more accurate results.
  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