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Thyroid Stimulating Hormone (TSH) with Immunoassay Method

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

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

Quick summary

["Your TSH levels help 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
35134-6
Short code
TSH Ab Ser Ql
Synonyms
TSH Ab 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 Matters

Thyroid hormones control many body processes, including energy use, digestion, and brain development. TSH signals your thyroid gland to produce or release these hormones. Abnormal levels can indicate conditions like hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid).

What to Expect Before the Test

No special preparation is needed for this blood test. You may have fasting instructions depending on your doctor’s protocol, but they will provide clear guidance. Wear comfortable clothing and plan to stay near the testing site for about 15 minutes.

How the Test Works

A healthcare professional will draw blood from a vein in your arm. The blood sample is sent to a lab where it is analyzed using an immunoassay to detect TSH levels. This method is precise and sensitive, helping to detect even small changes in hormone levels.

What the Results Mean

Results are typically reported in international units per liter (IU/L). High TSH levels often suggest hypothyroidism, while low levels may indicate hyperthyroidism. Your doctor will interpret results in the context of your medical history and symptoms.

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

Short name

TSH Level

Frequently asked questions

What does a high TSH level mean?
A high TSH level usually means your thyroid isn’t producing enough hormones, which can lead to fatigue, weight gain, cold intolerance, or depression. It’s often a sign of hypothyroidism and may require treatment like thyroid hormone medication.
What does a low TSH level mean?
A low TSH level may indicate your thyroid is overactive, causing symptoms like weight loss, anxiety, rapid heartbeat, or heat intolerance. This condition, called hyperthyroidism, can also be treated with medication or other therapies.
Can TSH levels change over time?
Yes, TSH levels can fluctuate due to various factors, including stress, pregnancy, certain medications, or underlying health conditions. Regular monitoring is important for people with thyroid disorders or those at risk for thyroid issues.
  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