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Thyroid Stimulating Hormone (TSH) with Serum Specimen

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

This blood test measures your thyroid-stimulating hormone, a key hormone that regulates your thyroid gland’s activity. It helps assess whether your thyroid is working normally.

Quick summary

["TSH helps diagnose thyroid disorders, including underactive (hypothyroidism) or overactive (hyperthyroidism) thyroid conditions."]

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

Key facts at a glance

LOINC
50540-4
Short code
TSH sp8 SerPl-aCnc
Synonyms
TSH sp8 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 check for thyroid problems, especially if you have symptoms like fatigue, weight changes, or unexplained mood swings. It’s also used to monitor thyroid function after treatment for thyroid disorders.

What to Expect Before the Test

No special preparation is needed, but avoid smoking or drinking alcohol 24 hours before the test. Fasted testing isn’t required, but eating a normal meal beforehand is fine.

How the Test Works

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

Possible Results and Interpretation

Results are compared to standard ranges, but individual results can vary. High TSH levels may suggest hypothyroidism, while low levels may indicate hyperthyroidism. 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 Level

Frequently asked questions

What does a high TSH level mean?
A high TSH level often signals an underactive thyroid (hypothyroidism), where your thyroid isn’t producing enough hormones. This can lead to fatigue, weight gain, or depression.
What does a low TSH level mean?
A low TSH level may indicate an overactive thyroid (hyperthyroidism), where your thyroid produces too much hormone. Symptoms can include weight loss, anxiety, or rapid heartbeat.
Can diet affect TSH test results?
Diet alone doesn’t directly affect TSH levels, but certain foods (like soy or goitrogens) may interact with thyroid function. Avoiding excessive iodine intake (e.g., from supplements) can help prevent false results.
  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