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Thyroid Hormone, Total (Serum or Plasma)

Published: August 9, 2026Updated: August 17, 2026

This test measures the total amount of thyroxine (T3) in your blood. T3 is a hormone produced by your thyroid gland that helps regulate metabolism.

Quick summary

["Your doctor may order this test to check thyroid function or monitor treatment for thyroid disorders."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
98015-1
Short code
T3 sp1 p chal SerPl-sCnc
Synonyms
T3 sp1 p chal SerPl-sCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
80
Ref high
200
Critical range
20 N/A – 400 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
84436
SNOMED
302346007
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 Does This Test Measure?

Total T3 includes both active and inactive forms of the hormone in your blood. It reflects how much T3 your body produces and releases into circulation.

Why Might You Need This Test?

Doctors often order total T3 testing when they suspect thyroid issues, such as hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid), or to evaluate thyroid hormone levels during treatment.

How Is This Test Performed?

A blood sample is taken from a vein in your arm. The sample is sent to a lab where it is analyzed using a specialized immunoassay method to measure the total T3 concentration.

What Are Common Uses?

This test helps diagnose and manage thyroid disorders, assess thyroid hormone levels in patients with known thyroid conditions, and monitor treatment effectiveness.

Reference range

Adult: 80-200 ng/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

Total T3

Frequently asked questions

What does a low total T3 level mean?
A low total T3 level may suggest your thyroid isn’t producing enough hormones, which could be due to an underactive thyroid (hypothyroidism) or other conditions affecting hormone production.
Can I eat or drink anything before this test?
You may eat and drink normally before this test unless your doctor instructed otherwise. Avoiding certain medications or supplements for a specified period may also be advised by your healthcare provider.
How long does it take to get results?
Results from this test are typically available within a few days to a week, depending on your lab’s processing schedule. Your doctor will discuss the results with you during your follow-up visit.
  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 17, 2026. · Read our editorial policy