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Thyroid Stimulating Hormone (TSH) with Serum Immunoassay

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

This test measures the amount of thyroid-stimulating hormone in your blood, which helps your thyroid gland produce hormones that regulate metabolism.

Quick summary

["TSH helps doctors check thyroid function and diagnose conditions like hypothyroidism or hyperthyroidism."]

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

Key facts at a glance

LOINC
29574-1
Short code
TSH DBS Ql
Synonyms
TSH DBS 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

What Is TSH Used For?

Your doctor may order a TSH test to evaluate thyroid health, especially if you have symptoms like fatigue, weight changes, or unexplained issues with metabolism. It’s also used during pregnancy to monitor thyroid function, which is critical for fetal development.

How Is the Test Performed?

A small blood sample is taken from your arm, usually in a doctor’s office or lab. The sample is processed to measure TSH levels using an immunoassay method, which detects the hormone in your serum.

What Are Common Symptoms to Watch For?

High TSH levels may suggest hypothyroidism (underactive thyroid), while low TSH levels could indicate hyperthyroidism (overactive thyroid). Symptoms may include fatigue, weight changes, or mood swings, but some people have no symptoms at all.

When Might You Need Follow-Up?

If your TSH results are outside normal ranges, your doctor may recommend retesting or additional thyroid function tests (like free T4) to determine the best course of action, such as medication or further evaluation.

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

Frequently asked questions

Why might my TSH test be done during pregnancy?
During pregnancy, thyroid function is crucial for fetal development. TSH testing helps ensure your thyroid is working properly, as thyroid hormones play a role in your baby’s growth and brain development.
What could affect my TSH test results?
Several factors may influence TSH levels, including certain medications (like lithium or amiodarone), thyroid disorders, pregnancy, or stress. It’s important to discuss all medications and health conditions with your doctor before testing.
Can I eat or drink before this test?
For most TSH tests, fasting is not required, but you should avoid caffeine or heavy meals before the blood draw if instructed by your healthcare provider. Follow their specific guidelines to ensure accurate results.
  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