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Thyroid Stimulating Hormone (TSH) with Immunoassay Method

Published: August 9, 2026Updated: August 17, 2026

This test measures the level of thyroid-stimulating hormone in your blood, which helps your body regulate thyroid hormone production.

Quick summary

["Your TSH level helps doctors check if your thyroid is working properly."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
102577-4
Short code
Cultivated Rye IgE RAST
Synonyms
Cultivated Rye IgE RAST
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
10
Ref high
40
Critical range
— – 500 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
rast
CPT
84484
SNOMED
302774002
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 diagnose or monitor thyroid conditions, such as hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid). It’s often the first test used to check thyroid function, especially if you have symptoms like fatigue, weight changes, or unexplained mood swings.

What Does a TSH Test Tell You?

A TSH test measures the amount of TSH in your blood. TSH is a hormone produced by your pituitary gland that signals your thyroid to make more or less thyroid hormone. High TSH levels often indicate hypothyroidism, while low levels may suggest hyperthyroidism or other issues.

How Is This Test Done?

A blood sample is taken from a vein in your arm, usually in a doctor’s office or lab. You may feel a small pinch, but it’s quick and doesn’t usually cause discomfort. The blood is then sent to a lab for testing.

What to Expect Before or After the Test

No special preparation is needed for this test. You can eat and drink normally before the blood draw. Afterward, you may experience mild bruising or soreness at the injection site, but this usually goes away quickly.

Reference range

Adult: 10-40 U/LN/A

Specimen: serum

No special preparation required. Avoid fatty meals before the test if possible.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

TSH (Serum)

Frequently asked questions

What does an abnormal TSH level mean?
If your TSH level is too high, it may mean your thyroid isn’t producing enough hormone (hypothyroidism), which can cause fatigue, weight gain, or depression. If it’s too low, it could indicate overactive thyroid (hyperthyroidism) or other conditions like pituitary problems.
How often should I get this test?
Your doctor will determine how often you need a TSH test based on your health, symptoms, and any treatments you’re on. For example, people with thyroid disease may need regular follow-ups to monitor their levels.
Can I eat or drink anything before the test?
No special diet or fasting is required for this test. You can eat and drink normally before your blood draw.
  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 17, 2026. · Read our editorial policy