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Thyroid Stimulating Hormone (TSH) with Immunoassay Method

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

This blood test measures your thyroid-stimulating hormone (TSH), a key hormone that regulates your thyroid function. It helps assess whether your thyroid is working normally.

Quick summary

["TSH helps doctors check for thyroid problems, including underactive (hypothyroidism) or overactive (hyperthyroidism) thyroid conditions."]

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

Key facts at a glance

LOINC
14919-5
Short code
TSH BII Ser Ql
Synonyms
TSH BII Ser Ql
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. Common reasons include unexplained fatigue, weight changes, or symptoms like cold sensitivity, dry skin, or depression. It’s also used to check for thyroid cancer or evaluate thyroid function before or after treatment.

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 broader thyroid panel. Wear comfortable clothing and plan to rest after the draw.

How the Test Works

A small blood sample is taken from a vein in your arm. The sample is sent to a lab where an immunoassay detects TSH levels in your serum. The result tells your doctor how your thyroid is functioning.

What the Results Mean

High TSH levels often suggest hypothyroidism, while low levels may indicate hyperthyroidism or other conditions. Your doctor will interpret results in relation to your symptoms and medical history.

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 too high?
High TSH levels are most commonly due to hypothyroidism (underactive thyroid), but they can also result from pituitary disorders, thyroiditis, or certain medications. Rarely, genetic factors or autoimmune diseases may play a role.
What causes TSH levels to be too low?
Low TSH levels often signal hyperthyroidism (overactive thyroid), but they can also occur with pituitary tumors, thyroid cancer, or thyroiditis. Stress, pregnancy, or thyroid medications can temporarily lower TSH as well.
How often should I get a TSH test?
Your doctor will determine how often you need testing based on your symptoms, medical history, and treatment plan. Some people with thyroid conditions may need regular follow-ups, while others may only need testing once or twice a year.
  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