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Thyroid Stimulating Hormone (TSH) with Serum/Plasma Screening Test

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

["A TSH screen helps detect thyroid hormone imbalances that may affect energy, weight, or mood."]

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

Key facts at a glance

LOINC
55362-8
Short code
TSH pre chal SerPl-aCnc
Synonyms
TSH pre 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 screen if you have symptoms like fatigue, weight changes, or unexplained mood swings. It’s also used as part of routine check-ups or when evaluating conditions like hypothyroidism or hyperthyroidism.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the test if your blood is drawn early in the morning. Wear comfortable clothing for easy access to your arm.

How the Test Works

A small sample of your blood (serum or plasma) is collected via a vein in your arm. The sample is then analyzed to measure the amount of TSH in your blood.

What the Results Mean

Results help determine if your thyroid is producing too much or too little hormone. Abnormal levels may indicate conditions that require further testing or treatment.

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.

Low TSH levels often suggest hypothyroidism (underactive thyroid), while high TSH levels may indicate hyperthyroidism (overactive thyroid) or other thyroid disorders. This test is a first step in diagnosing thyroid-related issues and guiding further evaluation if needed.

Short name

TSH Screen

Frequently asked questions

When might I get a follow-up test?
If your TSH screen result is outside the expected range, your doctor may order additional tests, such as free thyroxine (T4) or antithyroid antibodies, to get a clearer picture of your thyroid health.
What if I have symptoms but my TSH is normal?
Even if your TSH is within the normal range, other thyroid-related symptoms may still warrant further evaluation. Your doctor may recommend additional tests to check for conditions like subclinical hypothyroidism or other thyroid dysfunctions.
Can diet or supplements affect my TSH test results?
Certain medications (like some antidepressants or thyroid medications) or dietary supplements (e.g., soy, selenium) may influence thyroid hormone levels. Always inform your doctor about all medications or supplements you’re taking before the test.
  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