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Thyroid-stimulating hormone (TSH) mass concentration in serum/plasma

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 control metabolism, energy, and other bodily functions.

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
27975-2
Short code
TSH SerPl-mCnc
Synonyms
TSH SerPl-mCnc
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 diagnose or monitor thyroid disorders, such as hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid). It’s often the first test for thyroid issues because it’s sensitive and reliable.

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 lab requires it. Bring any medications you’re taking, as some (like thyroid hormone replacement) can affect results.

How the Test Works

A blood sample is drawn from a vein in your arm. The sample is sent to a lab where it’s analyzed to measure TSH levels using an immunoassay method, which detects the hormone in your blood.

What the Results Mean

Results are interpreted based on your symptoms and other tests. Low TSH may suggest hypothyroidism, while high TSH could indicate an underactive thyroid or other conditions. Your doctor will discuss findings with you.

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 (Serum/Plasma)

Frequently asked questions

What causes abnormal TSH results?
Abnormal TSH levels can result from thyroid diseases (e.g., Hashimoto’s disease or Graves’ disease), pituitary disorders, pregnancy, or certain medications. Other factors like stress, thyroid surgery, or radiation therapy may also affect results.
How often should I get this test?
Your doctor will determine how often you need retesting based on your health history, symptoms, and treatment plan. Regular follow-ups may be recommended if you have a thyroid condition or take thyroid hormone medication.
Can diet or supplements affect TSH test results?
Some medications (e.g., thyroid hormone drugs, lithium) or supplements (e.g., selenium) can influence TSH levels. Avoiding certain foods (like soy products) or supplements that may interact with thyroid function may be advised by your doctor.
  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