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Thyroid-stimulating hormone (TSH) measured by immunoassay (serum/plasma)

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

This test checks your thyroid gland’s ability to make hormones by measuring the amount of TSH in your blood. TSH is a hormone produced by the pituitary gland to regulate thyroid function.

Quick summary

["TSH helps balance your body’s energy and metabolism."]

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

Key facts at a glance

LOINC
3017-1
Short code
TSH BII Ser-mCnc
Synonyms
TSH BII Ser-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 Is This Test Done?

Your doctor may order a TSH test to check for thyroid problems, such as hypothyroidism (when your thyroid isn’t working enough) or hyperthyroidism (when it’s overactive). It’s also used to monitor treatment for thyroid conditions or screen for thyroid issues during pregnancy or other health concerns.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for 8–12 hours before the test if it’s part of a more complex evaluation. Bring any medications you’re taking to your appointment.

What Happens During the Test?

A small needle is used to draw blood from a vein in your arm. The blood sample is sent to a lab for analysis. The process takes a few minutes, and you may feel slight discomfort, but it’s usually over quickly.

What the Results Mean

Results help determine whether your thyroid is functioning normally. Abnormal levels may signal the need for further testing or treatment, but your doctor will interpret the results in the context of your overall health.

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’s Role in Health

Short name

TSH

Frequently asked questions

How long does it take to get my TSH results back?
Results are typically available within 1–3 business days, depending on your lab. Your doctor will contact you once they’re ready for review.
Can I eat or drink before this test?
If fasting is required (e.g., for a full thyroid panel), avoid food and liquids except water for 8–12 hours before testing. Otherwise, you can eat normally unless instructed otherwise.
What if my TSH level is too high or too low?
High TSH often means hypothyroidism, while low TSH may suggest hyperthyroidism. Your doctor will discuss symptoms, other test results, and possible next steps, such as additional blood tests or treatment options.
  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