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Total triiodothyronine (T3) concentration in serum

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

This test measures the amount of active thyroid hormone (T3) in your blood serum. T3 plays a key role in regulating metabolism, energy levels, and growth.

Quick summary

["Your doctor may order this test to check thyroid function or monitor thyroid hormone levels."]

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

Key facts at a glance

LOINC
14930-2
Short code
T3 SerPl-sCnc
Synonyms
T3 SerPl-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
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 Might This Test Be Done?

A healthcare provider may recommend this test if you have symptoms like fatigue, weight changes, or unexplained issues with metabolism. It could also be part of routine thyroid function testing or follow-up for thyroid disorders.

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 it’s part of a broader thyroid panel. Bring any medications you’re currently taking to your appointment.

How the Test Works

A blood sample is drawn from a vein in your arm. The sample is processed to measure T3 levels using a sensitive immunoassay method, which detects the hormone’s presence and concentration in your serum.

What the Results Mean

Results help determine if your thyroid is producing enough T3, which can indicate conditions like hypothyroidism (low T3) or hyperthyroidism (high T3). Your doctor will compare your results to your clinical picture 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.

Clinical Significance: Understanding T3 Levels

Short name

T3 Serum

Frequently asked questions

How accurate are my test results?
Test results are generally reliable, but accuracy depends on proper sample handling, timing, and lab quality. If you have recent thyroid medications or conditions, discuss them with your doctor to ensure accurate interpretation.
Can diet or supplements affect T3 levels?
Certain foods (like soy or selenium-rich foods) and supplements (e.g., iodine) can influence thyroid hormone levels. Avoid large amounts of these before testing if instructed by your provider.
What if my T3 level is outside the normal range?
If your T3 level is abnormal, your doctor may order additional tests (like T4 or thyroid-stimulating hormone) or recommend treatment adjustments. Follow-up may include monitoring symptoms and retesting as needed.
  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