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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

["Your doctor may order this test to check thyroid function or evaluate symptoms of thyroid disorders."]

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

Key facts at a glance

LOINC
12955-1
Short code
T3 sp4 p chal SerPl-mCnc
Synonyms
T3 sp4 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 This Test Might Be Ordered

Your healthcare provider may recommend a total T3 test if you have symptoms like fatigue, weight changes, or unexplained heart issues, or if you have a known thyroid condition. It could also be part of routine thyroid function testing or monitoring for conditions like hypothyroidism or hyperthyroidism.

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 blood draw if your test is part of a broader thyroid panel. Bring any medications you’re currently taking to your appointment.

What the Test Measures

Total T3 reflects the combined levels of free (active) T3 and protein-bound T3 in your blood. While free T3 is the biologically active form, total T3 provides a broader picture of thyroid hormone availability.

How the Test Results Are Used

Results help assess whether your thyroid is producing enough T3 to support normal bodily functions. Abnormal levels may indicate thyroid dysfunction, which could require further evaluation or treatment adjustments.

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 hypothyroidism (underactive thyroid), where the thyroid isn’t producing enough hormones, or conditions like chronic kidney disease that affect hormone metabolism.
What does a high total T3 level mean?
A high total T3 level could indicate hyperthyroidism (overactive thyroid), thyroiditis (inflammation of the thyroid), or rare conditions like thyroid storm. It may also be seen in certain medications or lab errors.
How often should I get this test?
Your doctor will determine the frequency based on your health status, symptoms, or treatment plan. Regular monitoring may be needed if you have thyroid disorders or take thyroid medications.
  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