Skip to content

Thyroid Stimulating Hormone (TSH) with Serum/Plasma Measurement

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 function.

Quick summary

["TSH helps your doctor check if your thyroid is working normally."]

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

Key facts at a glance

LOINC
12947-8
Short code
TSH sp8 p chal SerPl-aCnc
Synonyms
TSH sp8 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

Your doctor may order a TSH test to diagnose or monitor thyroid conditions, such as hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid). It’s often the first test for thyroid issues because TSH levels can be sensitive to changes in thyroid function.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for 8–12 hours before the test if it’s drawn early in the morning. Wear comfortable clothing for a blood draw.

What the Test Results Mean

Results can indicate whether your thyroid is producing too much or too little hormone. High TSH often suggests hypothyroidism, while low TSH may suggest hyperthyroidism or other conditions. Your doctor will interpret results in the context of your symptoms and other tests.

Common Conditions This Test Helps Diagnose

TSH testing is critical for diagnosing thyroid disorders, including Hashimoto’s disease (autoimmune hypothyroidism), Graves’ disease (hyperthyroidism), and thyroid nodules. It can also help monitor treatment for thyroid conditions or screen for thyroid dysfunction during pregnancy.

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 might cause my TSH levels to be abnormal?
Abnormal TSH levels can result from thyroid diseases, pituitary disorders, or other conditions like pregnancy, certain medications (e.g., lithium), or thyroid surgery. Symptoms like fatigue, weight changes, or hair loss may prompt testing.
How often should I get this test?
Frequency depends on your health status. If you have a thyroid condition, your doctor may recommend regular monitoring. Otherwise, it’s usually ordered only when symptoms or other tests suggest thyroid dysfunction.
Can diet or lifestyle affect TSH test results?
Dietary changes (e.g., iodine intake) or stress can influence thyroid function, indirectly affecting TSH. Avoiding extreme dieting, thyroid medications, or iodine supplements before testing may help ensure accurate 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