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Thyroid Stimulating Hormone (TSH) – Serum

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

This test measures the amount of thyroid-stimulating hormone in your blood. TSH is a hormone produced by your pituitary gland that helps regulate your thyroid function.

Quick summary

["TSH helps check if your thyroid is working properly and supports thyroid hormone balance."]

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

Key facts at a glance

LOINC
3015-5
Short code
TSH Bld-aCnc
Synonyms
TSH Bld-aCnc
Category
chemistry
Sample
whole-blood
Container
Lavender-top (EDTA)
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
3 mL
Stability
Room temperature: 4h, Refrigerated: 24h
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why This Test Is Done

Your doctor may order a TSH test to evaluate thyroid function, diagnose conditions like hypothyroidism or hyperthyroidism, or monitor treatment for thyroid disorders. It’s often the first test used to screen for thyroid issues due to its sensitivity and ease.

What to Expect Before the Test

No special preparation is needed for this test. You may have a small needle inserted into a vein in your arm, and a blood sample will be drawn. If you’re on thyroid medication, check with your doctor first to confirm whether to stop temporarily or adjust timing.

What the Results Mean

TSH levels can vary based on your overall health, age, and medications. High levels may suggest hypothyroidism (underactive thyroid), while very low levels could indicate hyperthyroidism (overactive thyroid). Your doctor will interpret results in the context of your symptoms and medical history.

Common Conditions Linked to TSH

Abnormal TSH levels can signal thyroid disorders, such as Hashimoto’s disease (autoimmune hypothyroidism), Graves’ disease (hyperthyroidism), or thyroid nodules. It can also help detect subclinical thyroid dysfunction before symptoms appear.

Reference range

Adult: 0.4-4.0 mIU/LN/A

Specimen: whole-blood

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.

TSH is a critical marker for thyroid health because it directly influences metabolism, energy levels, and overall well-being. Persistently high or low TSH may require further testing, like measuring free T4 or antibodies, to pinpoint the exact cause and guide treatment.

Short name

TSH Blood Test

Frequently asked questions

What causes TSH levels to be too high?
High TSH levels are often linked to hypothyroidism, where the thyroid gland doesn’t produce enough hormones. This can result from conditions like Hashimoto’s thyroiditis, pituitary issues, or iodine deficiency. Rarely, it may also occur with certain medications or pregnancy.
What causes TSH levels to be too low?
Low TSH levels may indicate hyperthyroidism, where the thyroid produces too much hormone. Causes can include Graves’ disease, thyroid nodules, or pituitary tumors. Other factors like thyroiditis (temporary inflammation) or excess thyroid medication can also lead to low TSH.
Can TSH levels change with age?
Yes, TSH levels can shift with age. Older adults may naturally have slightly higher TSH due to slower thyroid function. However, if symptoms like fatigue or weight changes appear, a TSH test can help check for underlying thyroid issues that may need treatment.
  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