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Triiodothyronine (T3), Whole Blood

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

A blood test that measures triiodothyronine (T3), a thyroid hormone that helps regulate the body's energy use, metabolism, and other functions.

Quick summary

["T3 is one of the main thyroid hormones and is usually interpreted together with T4 and thyroid-stimulating hormone (TSH)."]

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

Key facts at a glance

LOINC
57741-1
Short code
LPT OKT3 Bld-nRate
Synonyms
LPT OKT3 Bld-nRate
Category
thyroid
Sample
whole-blood
Container
Lavender-top (EDTA)
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
85610
SNOMED
396252006
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

What is this test?

This test measures the amount of triiodothyronine (T3) in a blood sample. T3 works with thyroxine (T4) to regulate metabolism, energy use, heart function, and other body processes.

Why might I need this test?

A T3 test may be ordered to help evaluate thyroid function, especially when symptoms suggest an overactive or underactive thyroid. It is commonly reviewed with T4 and thyroid-stimulating hormone (TSH), rather than by itself.

How is the test performed?

A healthcare professional draws blood from a vein, usually in the arm. The laboratory measures T3 using a validated blood-testing method and sends the result to your healthcare provider.

How do I prepare for the test?

Follow the preparation instructions provided by your healthcare professional. Tell the laboratory if you are taking thyroid medicines, iodine or biotin supplements, or other medications that could affect the result.

Reference range

Adult: 80-200 ng/dLN/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.

◆Associated findings1

Short name

T3

Frequently asked questions

What does T3 measure?
T3 measures triiodothyronine, one of the principal hormones produced by the thyroid gland.
Is this the same as a free T3 test?
No. A T3 test may measure total T3 or free T3, which reflects different portions of the hormone. The exact method and reporting format should be confirmed on the laboratory report.
Do I need to fast before this test?
Fasting is often unnecessary, but your healthcare professional may give specific instructions based on the laboratory and your health history.
  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