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Thyroid Stimulating Hormone (TSH) with Serum/Plasma Measurement

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

This blood test measures your thyroid-stimulating hormone, a key hormone that helps regulate your metabolism and thyroid function.

Quick summary

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

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

Key facts at a glance

LOINC
58833-5
Short code
TSH 20M pre chal SerPl-mCnc
Synonyms
TSH 20M pre chal SerPl-mCnc
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 disorders, such as hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid). It’s often the first test used to check thyroid function, especially if you have symptoms like fatigue, weight changes, or unexplained mood swings.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the blood draw if your test is part of a metabolic panel. Wear comfortable clothing and plan for the test to take about 5 minutes. Bring any medications you’re currently taking, as some may 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 indicate hypothyroidism, while low levels may suggest hyperthyroidism or other conditions. Your doctor will interpret results in relation to your symptoms and other tests.

Common Conditions Linked to TSH

Abnormal TSH levels can signal thyroid diseases like Hashimoto’s disease (autoimmune hypothyroidism) or Graves’ disease (autoimmune hyperthyroidism). It may also be used to evaluate thyroid nodules, pituitary disorders, or thyroid cancer.

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.

TSH is highly sensitive and specific for thyroid function, making it a first-line test for thyroid disorders. It helps guide treatment decisions, such as starting thyroid hormone replacement for hypothyroidism or managing conditions like pituitary adenomas that affect TSH production.

Short name

TSH Level

Frequently asked questions

What causes TSH levels to be too high?
High TSH levels are most commonly caused by hypothyroidism, where the thyroid gland doesn’t produce enough hormone. Other possible causes include pituitary disorders (e.g., pituitary tumors), autoimmune thyroiditis, or certain medications that affect thyroid function.
What causes TSH levels to be too low?
Low TSH levels can result from hyperthyroidism (e.g., Graves’ disease), thyroid nodules, or pituitary issues that reduce TSH production. Rarely, it may also occur with thyroiditis (inflammation of the thyroid) or excessive thyroid hormone intake.
How often should I get a TSH test?
Your doctor will determine how often you need retesting based on your symptoms, medical history, and treatment plan. For example, people with hypothyroidism may need periodic monitoring, while those with stable thyroid function may only need testing if symptoms change or if you’re pregnant.
  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