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Thyroid Stimulating Hormone (TSH) with Serum Specimen

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 gland’s activity, which affects metabolism, energy levels, and overall health.

Quick summary

["TSH helps your thyroid work properly—low or high levels may signal thyroid issues."]

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

Key facts at a glance

LOINC
50533-9
Short code
TSH sp1 SerPl-aCnc
Synonyms
TSH sp1 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

Doctors order TSH tests to check for thyroid problems, such as hypothyroidism (when your thyroid isn’t working enough) or hyperthyroidism (when it’s overactive). It’s often the first test for thyroid function, especially if you have symptoms like fatigue, weight changes, or unexplained issues.

How the Test Works

A small blood sample is taken from your arm and sent to a lab. The lab uses an immunoassay (a sensitive test that detects specific proteins) to measure TSH levels in your serum.

What to Expect Before the Test

No special preparation is needed, but you may want to avoid caffeine or alcohol before the test if it causes stress or affects your blood pressure.

Possible Results and Next Steps

Results are usually reported in microinternational units per liter (µIU/L). If your TSH is too high, it may indicate hypothyroidism. If it’s too low, it could suggest hyperthyroidism. Your doctor will discuss these findings with you and may recommend further tests or treatments.

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

What does a high TSH level mean?
A high TSH level often means your thyroid isn’t producing enough hormones, which can lead to symptoms like cold sensitivity, weight gain, or fatigue. It may signal hypothyroidism, a condition where the thyroid gland doesn’t function properly.
What does a low TSH level mean?
A low TSH level can indicate your thyroid is making too much hormone, which may cause symptoms like anxiety, rapid heartbeat, or weight loss. It could signal hyperthyroidism or other thyroid disorders.
Can TSH levels change over time?
Yes, TSH levels can fluctuate due to stress, illness, pregnancy, or certain medications. If your levels are abnormal, your doctor may retest or check for underlying causes like thyroid disease, pituitary issues, or other health conditions.
  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