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Thyroid Stimulating Hormone (TSH) with Serum/Plasma Measurement by Immunoassay

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

This test measures the amount of thyroid-stimulating hormone (TSH) in your blood. TSH helps regulate your thyroid hormone levels, which are important for energy, metabolism, and overall health.

Quick summary

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

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

Key facts at a glance

LOINC
12938-7
Short code
TSH 1.5h p chal SerPl-aCnc
Synonyms
TSH 1.5h 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 Is This Test Done?

Your doctor may order a TSH test to evaluate thyroid function. Common reasons include symptoms like fatigue, weight changes, or unexplained goiter (enlarged thyroid). It’s also used as part of routine thyroid screening or monitoring for conditions like hypothyroidism or hyperthyroidism.

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. Wear a comfortable shirt for easy access to your arm. If you’re on thyroid medication, check with your doctor first—some medications may affect results.

What Happens During the Test?

A healthcare professional will insert a small needle into a vein in your arm to draw blood. You may feel a brief pinch, but it’s usually over quickly. The blood sample is then sent to a lab for analysis.

What Do the Results Mean?

Results are interpreted based on your symptoms and medical history. Low TSH may suggest hyperthyroidism (overactive thyroid), while high TSH often indicates hypothyroidism (underactive thyroid). Your doctor will discuss findings with you in the context of your overall health.

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

How often should I get this test?
Your doctor will determine how often you need retesting based on your symptoms, medical history, and any treatments you’re receiving. For example, people with hypothyroidism may need TSH checks every few months to monitor treatment effectiveness.
Can diet or medications affect TSH test results?
Certain medications (e.g., some antidepressants, steroids, or thyroid medications) can influence TSH levels. Avoiding these temporarily may help ensure accurate results. Some foods, like soy or selenium-rich foods, may also interact with thyroid function—discuss with your doctor if you suspect dietary concerns.
What if my TSH result is outside the normal range?
If your TSH is elevated, you may have hypothyroidism and could benefit from thyroid hormone replacement therapy. If it’s low, you might have hyperthyroidism and could need medication to control symptoms. Your doctor will guide you on next steps, which may include additional tests or adjustments to your treatment plan.
  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