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Thyroid Stimulating Hormone (TSH) with Confirmatory Immunoassay (Serum)

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

This test measures your thyroid-stimulating hormone level in your blood to help check if your thyroid is working properly.

Quick summary

["TSH helps regulate your metabolism and supports energy levels; abnormal results may signal thyroid dysfunction."]

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

Key facts at a glance

LOINC
77623-7
Short code
TSH 2.5h p chal SerPl-aCnc
Synonyms
TSH 2.5h 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 this test if you have symptoms like fatigue, weight changes, or unexplained issues with metabolism. It’s also used to monitor thyroid conditions like hypothyroidism or hyperthyroidism, especially after treatment for these disorders.

What to Expect Before the Test

No special preparation is needed, but avoid taking thyroid medications (if applicable) for 24 hours before testing. Drink plenty of water and fast for 8–12 hours if instructed, as some labs require a fasting blood draw for TSH.

What the Results Mean

TSH levels can vary based on your health, age, and medications. High levels may indicate hypothyroidism (underactive thyroid), while very low levels could suggest hyperthyroidism (overactive thyroid). Your doctor will interpret results in the context of your symptoms and medical history.

Common Causes of Abnormal Results

Changes in TSH can occur due to thyroid disease, pregnancy, certain medications (e.g., lithium), or conditions like pituitary disorders. Stress, illness, or sleep deprivation may also temporarily affect hormone levels.

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 Confirmatory

Frequently asked questions

What does a high TSH level mean?
A high TSH level often signals hypothyroidism, where your thyroid isn’t producing enough hormones. This can lead to symptoms like weight gain, fatigue, or cold intolerance. Your doctor may recommend further testing or treatment to address the underlying cause.
What does a low TSH level mean?
A low TSH level may indicate hyperthyroidism (overactive thyroid) or a pituitary issue that suppresses TSH production. Symptoms could include weight loss, anxiety, or rapid heartbeat. Additional tests, like free T4 or antibody checks, may be needed to diagnose the cause.
How often should I get this test?
The frequency depends on your medical condition. If you have a diagnosed thyroid disorder, your doctor may recommend regular monitoring (e.g., every 6–12 months). If you’re asymptomatic, this test may only be done if symptoms return or if you have risk factors (e.g., family history of thyroid disease).
  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