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Thyroid hormone total triiodothyronine (T₃) in serum/plasma

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

This test measures the total amount of the hormone triiodothyronine (T₃) in your blood, which plays a key role in regulating metabolism and energy levels.

Quick summary

["Total T₃ helps assess thyroid function and identify potential thyroid disorders."]

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

Key facts at a glance

LOINC
12958-5
Short code
T3 sp7 p chal SerPl-mCnc
Synonyms
T3 sp7 p chal SerPl-mCnc
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

Why Is This Test Done?

Your healthcare provider may order this test if you have symptoms of thyroid issues, such as fatigue, weight changes, or irregular heartbeats. It may also be used to monitor thyroid treatment or diagnose conditions like hypothyroidism or hyperthyroidism.

What Does It Measure?

Total T₃ reflects the combined levels of active and inactive forms of the hormone in your blood. While thyroxine (T₄) is more abundant, T₃ is metabolically more active and can influence energy and body temperature more directly.

How Is It Collected?

A blood sample is taken from a vein, usually in your arm. The blood is then processed to separate serum or plasma for testing.

What Are Common Results?

Results are not provided with specific reference ranges here, as they vary by lab and individual health. Your results will be interpreted by your healthcare provider in the context of your symptoms and other tests.

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

How long does it take to get results?
Results are typically available within 1 to 3 business days, depending on your lab’s processing schedule.
What does a low or high total T₃ mean?
A low total T₃ level may indicate thyroid dysfunction, but it can also be influenced by other factors like stress, diet, or certain medications. A high level may signal overactive thyroid function or medication effects. Your provider will discuss these findings with you.
Can diet affect T₃ levels?
Yes, certain foods (e.g., soy, goitrogens) or supplements (e.g., selenium) can temporarily affect thyroid hormone levels. Avoiding these for a few days before testing may help ensure more 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 17, 2026. · Read our editorial policy