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Thyroid Stimulating Hormone (TSH) with Serum/plasma

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 activity, which affects metabolism, energy levels, and overall health.

Quick summary

["TSH helps doctors check if your thyroid is working normally."]

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

Key facts at a glance

LOINC
12945-2
Short code
TSH sp6 p chal SerPl-aCnc
Synonyms
TSH sp6 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 thyroid problems, such as hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid). It’s often the first test used because TSH levels can be very sensitive to thyroid changes.

What to Expect Before the Test

No special preparation is needed for this blood test. You may have a small needle inserted into your arm or hand to draw blood. If you’re on thyroid medication, let your doctor know before the test, as it could affect results.

What the Results Mean

TSH results help determine whether your thyroid is producing too much or too little hormone. High TSH levels often suggest hypothyroidism, while low levels may indicate hyperthyroidism. Your doctor will interpret results in the context of your symptoms and other tests.

Common Conditions This Test Helps Diagnose

This test is commonly used to diagnose or manage conditions like Hashimoto’s disease (an autoimmune thyroid disorder), Graves’ disease (another autoimmune thyroid disorder), or thyroid nodules. It can also help monitor treatment for thyroid disorders.

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 causes high TSH levels?
High TSH levels are most commonly caused by hypothyroidism, where the thyroid gland doesn’t produce enough hormone. Other possible causes include pituitary disorders, certain medications (like lithium), or thyroid surgery or radiation treatment. Rarely, it can be due to genetic factors or thyroiditis (inflammation of the thyroid).
What causes low TSH levels?
Low TSH levels often signal hyperthyroidism, where the thyroid produces too much hormone. Causes may include Graves’ disease, thyroid nodules, or pituitary tumors. Other conditions, such as thyroiditis (temporary overactivity) or excessive iodine intake, can also lead to low TSH.
Can TSH levels change over time?
Yes, TSH levels can fluctuate due to changes in thyroid function, stress, pregnancy, or certain medications. If your doctor suspects a thyroid issue, they may repeat the test or order additional tests to get a clearer picture.
  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