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Thyroid Stimulating Hormone (TSH) with Serum/Plasma Concentration Measurement

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

This test measures the amount of thyroid-stimulating hormone in your blood, which helps regulate your thyroid function.

Quick summary

["Your TSH level 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
12939-5
Short code
TSH 2h p chal SerPl-aCnc
Synonyms
TSH 2h 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

A TSH test is often ordered to diagnose or monitor thyroid disorders, such as hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid). It may also be used during pregnancy, before surgery, or if you have symptoms like fatigue, weight changes, or unexplained hair loss.

What to Expect Before the Test

No special preparation is usually needed, but your doctor may advise you to avoid certain medications that could affect results. If you’re pregnant or breastfeeding, inform your healthcare provider before the test.

What Happens During the Test

A blood sample will be taken from a vein, typically in your arm. You may feel a slight pinch, but it usually doesn’t cause discomfort. The sample is sent to a lab for analysis.

What the Results Mean

Results are interpreted based on your symptoms, medical history, and other tests. High TSH levels often indicate hypothyroidism, while very low levels may suggest hyperthyroidism. Your doctor will discuss the results 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 Level

Frequently asked questions

How often should I get a TSH test?
TSH tests are typically done as needed—either for diagnosis, monitoring, or screening. Your doctor will determine how often you need retests based on your health status, symptoms, and any ongoing treatments.
What can affect my TSH test results?
Several factors may influence TSH levels, including certain medications (like lithium or amiodarone), pregnancy, stress, sleep deprivation, and thyroid-related conditions. If you’re taking medications or have recent changes in health, discuss them with your doctor.
What are the most common symptoms of abnormal TSH levels?
Symptoms of high TSH (hypothyroidism) may include fatigue, weight gain, cold intolerance, dry skin, and depression. Symptoms of low TSH (hyperthyroidism) may include weight loss, anxiety, rapid heartbeat, and heat intolerance. However, some people may have no symptoms at all.
  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