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Thyroid Stimulating Hormone (TSH) with Serum/Plasma Measurement

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

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

Quick summary

["Your TSH levels help diagnose or monitor thyroid disorders like hypothyroidism or hyperthyroidism."]

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

Key facts at a glance

LOINC
33259-3
Short code
TSH 1h p TRH SerPl-aCnc
Synonyms
TSH 1h p TRH 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
85610
SNOMED
396252006
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 Matters

TSH is a hormone produced by your pituitary gland that signals your thyroid to produce thyroid hormones (like thyroxine and triiodothyronine). Abnormal levels can indicate whether your thyroid is working too slowly or too quickly, which may cause fatigue, weight changes, or other symptoms.

How the Test Works

A small blood sample is taken from a vein in your arm. The sample is sent to a lab where it’s analyzed using an immunoassay method to detect TSH levels in your serum or plasma.

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 affects your symptoms. Wear comfortable clothing and bring a photo ID if required.

Common Symptoms Linked to TSH Results

High TSH levels may suggest hypothyroidism (underactive thyroid), causing fatigue, weight gain, or cold sensitivity. Low TSH levels may indicate hyperthyroidism (overactive thyroid), leading to anxiety, weight loss, or rapid heartbeat.

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 hypothyroidism, meaning your thyroid isn’t producing enough hormones. This can be caused by conditions like Hashimoto’s disease, thyroid removal, or iodine deficiency. Your doctor may recommend further tests or treatment to manage symptoms.
What does a low TSH level mean?
A low TSH level may suggest hyperthyroidism, where your thyroid produces too much hormone. Causes can include Graves’ disease, thyroid nodules, or pituitary tumors. Your doctor may check other thyroid hormones (like free T4) to confirm the diagnosis.
Can TSH levels change over time?
Yes, TSH levels can fluctuate due to stress, pregnancy, certain medications (like lithium or amiodarone), or thyroid-related conditions. Regular monitoring may be needed if you have an existing thyroid disorder or symptoms that persist.
  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