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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 hormone levels, which are important for metabolism, energy, and overall health.

Quick summary

["TSH helps your thyroid function and keeps your metabolism steady."]

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

Key facts at a glance

LOINC
29317-5
Short code
TSH 1h p chal SerPl-aCnc
Synonyms
TSH 1h 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 check for thyroid problems, such as hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid). It can also be used to monitor thyroid treatment or screen for thyroid-related conditions during pregnancy.

What to Expect Before the Test

No special preparation is usually needed. You may have a small needle inserted into your arm or hand to draw blood. If you’re taking thyroid medication, let your doctor know beforehand, as it may affect your results.

What the Results Mean

TSH levels can vary based on your health, age, and other factors. High TSH often suggests hypothyroidism, while very low TSH may indicate hyperthyroidism. Your doctor will interpret results in relation to your symptoms and medical history.

Common Reasons for Testing

TSH tests are commonly done if you have symptoms like fatigue, weight changes, or unexplained issues with mood or digestion. They’re also part of routine check-ups for people at higher risk of thyroid problems.

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 TSH levels to be abnormal?
Abnormal TSH levels can result from thyroid diseases (like Hashimoto’s disease or Graves’ disease), thyroid nodules, pituitary disorders, or certain medications. Stress, pregnancy, or thyroid surgery may also affect results.
How long does it take to get TSH test results?
Results are typically available within 1–3 business days, depending on your lab. Your doctor will discuss them with you during your follow-up visit.
Can diet or supplements affect TSH test results?
Some thyroid medications (like levothyroxine) can influence TSH levels. Avoiding caffeine or iodine-rich foods (like seaweed) for a few days before testing may reduce interference, but always follow your doctor’s advice.
  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