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Thyroid hormone total serum 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, energy levels, and other bodily functions.

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
12956-9
Short code
T3 sp5 p chal SerPl-mCnc
Synonyms
T3 sp5 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 this test if you have symptoms like fatigue, weight changes, or irregular heart rhythms, or if they suspect thyroid issues. It could also be part of routine thyroid function testing or follow-up 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 test if blood is drawn from a vein. If you’re taking thyroid medications, check with your doctor first to avoid missing doses.

How the Test Works

A small sample of your blood is drawn from a vein in your arm. The sample is then analyzed in a lab to measure the total T₃ levels in your serum.

What the Results Mean

Results help assess whether your thyroid is functioning normally. While reference ranges vary by lab, abnormal levels may indicate thyroid disorders or other health concerns that need further evaluation.

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 causes abnormal T₃ levels?
Abnormal T₃ levels can result from thyroid gland disorders (e.g., hypothyroidism or hyperthyroidism), medications (like amiodarone or steroids), iodine deficiency, or stress. Rarely, genetic conditions or thyroid cancer may also affect T₃ production.
How often should I get this test?
Your doctor will determine the frequency based on your health needs. For example, people with thyroid disorders may need regular monitoring, while others may only need it once or twice a year.
Can lifestyle changes affect T₃ levels?
Yes, diet (e.g., iodine intake), stress, sleep, and exercise can influence thyroid hormone levels. Avoiding excessive caffeine or alcohol before testing may help ensure 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