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Thyroid hormone total triiodothyronine (T3) concentration

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

This test measures the amount of total triiodothyronine (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
83125-5
Short code
T3 SerPl IA-sCnc
Synonyms
T3 SerPl IA-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
Method
ia
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 request a total T3 test to evaluate thyroid health, diagnose conditions like hypothyroidism or hyperthyroidism, or assess how well thyroid hormone replacement therapy is working. It can also be used alongside other thyroid tests to provide a fuller picture of your hormone levels.

What to Expect Before the Test

No special preparation is usually needed for this blood test. You may be asked to fast for 8–12 hours before the draw if your doctor recommends it, but this is not always required. Bring any medications you’re taking to your appointment.

What the Test Involves

A healthcare provider will draw blood from a vein in your arm using a small needle. You may feel a brief pinch, but the procedure is quick. The blood sample is then sent to a lab for analysis.

What the Results Mean

Results alone don’t provide a diagnosis—they’re used alongside other tests and clinical findings. Abnormal levels may signal thyroid dysfunction, but interpretation depends on your overall health and other test results.

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 symptoms might this test be checking for?
Symptoms like fatigue, weight changes, or unexplained anxiety could prompt a total T3 test, especially if you have a history of thyroid disease or symptoms like hair loss or muscle weakness.
How does this test differ from T4 tests?
Total T3 is a more direct measure of active thyroid hormone compared to T4 (thyroxine), which is converted to T3 in your body. Doctors may use both tests to assess thyroid function comprehensively.
What if my results are outside the normal range?
If your results are abnormal, your doctor will review them with you and may recommend additional tests (like free T3 or TSH) or adjustments to your treatment plan. Follow-up depends on your symptoms and medical 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