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Thyroid hormone total triiodothyronine (T₃) concentration

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

This test measures the total amount of the hormone triiodothyronine (T₃) in your blood. T₃ is a key thyroid hormone that helps regulate metabolism.

Quick summary

["Your body’s thyroid function and energy levels may be affected by T₃ levels."]

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

Key facts at a glance

LOINC
3054-4
Short code
T3True SerPl-mCnc
Synonyms
T3True 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 Is Done

Doctors may order this test to evaluate thyroid function, especially if you have symptoms like fatigue, weight changes, or unexplained heart issues. It’s often used alongside other thyroid tests, such as thyroid-stimulating hormone (TSH).

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before drawing blood. Wear a comfortable shirt for easy access to your arm.

What Happens During the Test

A healthcare provider will insert a small needle into your arm to draw blood. You may feel a slight pinch, but it usually takes only a few minutes. The blood sample is sent to a lab for analysis.

What the Results Mean

Results help determine if your thyroid is producing enough T₃. Abnormal levels may indicate conditions like hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid), though they’re often checked alongside TSH.

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 my T₃ test results?
Results are typically available within 1–3 business days, depending on your lab’s processing time. Follow up with your doctor to discuss the results and next steps.
Can diet or supplements affect T₃ levels?
Yes, certain foods (like goitrogens in cruciferous vegetables) or medications (e.g., iodine supplements) may influence thyroid hormone levels. Your doctor can guide you on how to prepare for the test without interference.
Is fasting required for this test?
No strict fasting is required, but avoiding caffeine or heavy meals 2 hours before the draw may improve accuracy. Always follow your lab’s specific instructions.
  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