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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, 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
11579-0
Short code
TSH SerPl DL<=0.05 mIU/L-aCnc
Synonyms
TSH SerPl DL<=0.05 mIU/L-aCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
0
Ref high
100
Critical range
0.1 N/A – 20 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
detection-limit-miu-l
CPT
83721
SNOMED
113079007
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?

Doctors may order a TSH test to diagnose or monitor thyroid disorders, such as hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid). It can also be used to screen for thyroid issues or check for conditions like pituitary gland problems or thyroid cancer.

What to Expect Before the Test

No special preparation is usually needed. You may be asked to fast for 8–12 hours before the test, but this depends on your doctor’s instructions. Bring any medications you’re currently taking, as some may affect results.

What Happens During the Test?

A healthcare professional will draw blood from a vein in your arm. You may feel a slight pinch, but it usually doesn’t cause much discomfort. The blood is then sent to a lab for analysis using an immunoassay method to measure TSH levels accurately.

What Do Results Mean?

Results can indicate whether your thyroid is producing too much or too little hormone. High TSH levels often suggest hypothyroidism, while low levels may signal hyperthyroidism or other thyroid-related issues. Your doctor will interpret results in relation to your symptoms and medical history.

Reference range

Optimal: <100 mg/dLN/A

Specimen: serum

Fasting for 12-14 hours preferred. Water is permitted. Avoid alcohol for 24 hours before the test.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

TSH Level

Frequently asked questions

How often should I get this test?
TSH testing frequency depends on your health status. If you have a known thyroid condition, your doctor may recommend regular monitoring. Otherwise, it’s often done as needed for symptoms or screening.
What if my TSH level is outside the normal range?
If your TSH level is abnormal, your doctor may recommend further testing, such as checking free thyroid hormones (like T3 or T4) or imaging studies to investigate the cause. Treatment options depend on whether you have hypothyroidism or hyperthyroidism.
Can diet or medications affect TSH test results?
Certain medications (e.g., thyroid hormone replacements, amiodarone, or lithium) can influence TSH levels. Some foods (like soy or selenium-rich foods) may also interact, so always inform your doctor about all medications and supplements you take.
  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