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Thyroid Stimulating Hormone (TSH) – Serum or Plasma Probe Test

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

This blood test measures your thyroid-stimulating hormone, a key hormone that regulates your metabolism and helps control how fast your body uses energy.

Quick summary

["TSH helps diagnose thyroid disorders by checking if your thyroid gland is working normally."]

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

Key facts at a glance

LOINC
101298-8
Short code
RSV RNA Throat Ql NAA+n-prb
Synonyms
RSV RNA Throat Ql NAA+n-prb
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
non-probe-amp-tar
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?

TSH is primarily used to screen for and monitor thyroid conditions, such as hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid). It’s often the first test doctors recommend when evaluating symptoms like fatigue, weight changes, or unexplained goiter.

How Is the Test Performed?

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

What Might Affect Results?

Several factors can influence TSH levels, including pregnancy, certain medications (like lithium or amiodarone), thyroid surgery, or radiation treatment. Stress, illness, or recent blood loss can also temporarily alter results.

Common Symptoms Linked to Abnormal TSH Levels

High TSH often signals hypothyroidism, causing symptoms like cold intolerance, dry skin, or weight gain. Low TSH may suggest hyperthyroidism, leading to anxiety, rapid heartbeat, or unintended weight loss.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

TSH plays a critical role in thyroid function. Elevated levels typically indicate an underactive thyroid, while low levels may point to an overactive thyroid. Since TSH is sensitive to thyroid feedback, it’s a reliable first step in diagnosing these conditions, though further tests (like free T4 or thyroid antibodies) may be needed for confirmation.

Short name

TSH

Frequently asked questions

Why might my doctor order a TSH test?
Your doctor may recommend a TSH test if you have symptoms like fatigue, weight changes, or unexplained goiter, or if you have a family history of thyroid disease. It’s also often included in routine check-ups for older adults or those with certain medical conditions.
Could TSH test results be affected by my diet or lifestyle?
While diet and lifestyle factors like iodine intake can influence thyroid function, they don’t directly affect TSH test results. However, maintaining a balanced diet and managing stress may help support overall thyroid health.
What if my TSH result is outside the normal range?
If your TSH result is outside the normal range, your doctor will likely follow up with additional tests (like free T4 or thyroid antibodies) to determine the cause. They may also recommend adjustments to your treatment plan if needed, such as medication or further monitoring.
  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