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Thyroid Stimulating Hormone (TSH) with Serum/plasma Specimen, Immunoassay Method

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

This test measures your thyroid-stimulating hormone, a key hormone that regulates your thyroid function and metabolism. It helps doctors diagnose and monitor thyroid disorders.

Quick summary

["Your TSH level helps assess whether your thyroid is working too slowly or too quickly."]

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

Key facts at a glance

LOINC
12936-1
Short code
TSH 40M p chal SerPl-aCnc
Synonyms
TSH 40M p chal SerPl-aCnc
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 check for thyroid problems, such as hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid). It’s often the first test used to evaluate thyroid function, especially if you have symptoms like fatigue, weight changes, or unexplained mood swings.

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 your blood is drawn early in the morning. If you’re taking thyroid medication, your doctor may instruct you to stop taking it temporarily or adjust your timing.

What the Test Results Mean

TSH levels can vary based on your health, age, and other factors. High levels may indicate hypothyroidism, while very low levels could suggest hyperthyroidism. Your doctor will interpret the results in relation to your symptoms and medical history.

Common Conditions This Test Helps Diagnose

This test is commonly used to diagnose or monitor conditions like Graves’ disease, Hashimoto’s thyroiditis, pituitary disorders, and thyroid nodules. It can also help evaluate thyroid function in people with symptoms like hair loss, depression, or unexplained weight changes.

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 could cause abnormal TSH levels?
Abnormally high TSH levels may be due to hypothyroidism, pituitary disorders, or certain medications. Low TSH levels can result from hyperthyroidism, thyroid tumors, or pituitary issues. Other factors, like pregnancy, stress, or thyroid surgery, can also affect TSH levels.
How often should I get this test?
Your doctor will determine how often you need this test based on your medical history, symptoms, and treatment plan. Some people with stable thyroid conditions may need it yearly, while others may require more frequent monitoring.
Can I take anything before or after the test?
If your doctor instructed you to stop thyroid medication before the test, follow their guidance carefully. Avoid smoking or drinking alcohol before the test, as they can affect results. If you have any questions, ask your healthcare provider.
  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