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 in your blood, which helps your thyroid gland produce hormones that regulate metabolism, energy, and overall health.

Quick summary

["TSH helps doctors check if your thyroid is working properly."]

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

Key facts at a glance

LOINC
12930-4
Short code
T4 sp9 p chal SerPl-mCnc
Synonyms
T4 sp9 p chal SerPl-mCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
4.5
Ref high
12
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
84436
SNOMED
302345006
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

What Is TSH Used For?

TSH is primarily used to diagnose and monitor thyroid disorders, such as hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid). It can also be part of routine check-ups for individuals with risk factors like family history of thyroid issues or symptoms like fatigue, weight changes, or sensitivity to heat/cold.

How Is This Test Performed?

A blood sample is taken from a vein, usually in your arm. The sample is sent to a lab where it is analyzed using an immunoassay method to measure TSH levels. Results are typically available within a few days.

What Might Affect Your Results?

Several factors can influence TSH levels, including medications (like thyroid hormone replacements), pregnancy, stress, certain medical conditions, and even the timing of blood collection. If you’re taking medications or have recent changes in health, let your healthcare provider know.

Common Reasons for Testing

Your doctor may order a TSH test if you have symptoms like unexplained weight changes, fatigue, depression, or changes in your menstrual cycle. It’s also used to screen for thyroid issues, especially in people with a family history of thyroid disease or those with autoimmune conditions.

Reference range

Adult: 4.5-12.0 μg/dLN/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

Why might my TSH test be done during pregnancy?
TSH is often checked during pregnancy because thyroid function is crucial for fetal development. Low or high TSH levels can indicate potential risks, such as miscarriage or developmental issues in the baby. Your doctor may recommend monitoring TSH levels if you have a history of thyroid problems or symptoms like fatigue or weight changes.
What if my TSH is outside the normal range?
If your TSH is too high, it may suggest an underactive thyroid (hypothyroidism), which can cause fatigue, weight gain, or depression. If it’s too low, it could indicate an overactive thyroid (hyperthyroidism), leading to symptoms like weight loss, anxiety, or rapid heartbeat. Your doctor will discuss further testing or treatment options based on your results.
Can lifestyle changes affect TSH levels?
Yes, lifestyle factors like diet (especially iodine intake), sleep, and stress can influence thyroid function. Avoiding excessive caffeine or iodine-rich foods before testing may help ensure accurate results. Always follow your doctor’s instructions for preparation.
  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