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Reverse Triiodothyronine (rT3), Serum/Plasma — HPLC

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

Measures reverse triiodothyronine (rT3), a form of thyroid hormone, in serum or plasma using high-performance liquid chromatography (HPLC).

Quick summary

["This blood test measures reverse T3 and may help clinicians evaluate thyroid hormone metabolism alongside other thyroid tests."]

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

Key facts at a glance

LOINC
17743-6
Short code
T3RU 1h p chal NFr SerPl
Synonyms
T3RU 1h p chal NFr SerPl
Category
thyroid
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

What is this test?

Reverse triiodothyronine, or rT3, is a form of the thyroid hormone T3. This test measures its concentration in serum or plasma using high-performance liquid chromatography (HPLC).

Why might I need this test?

Your clinician may order rT3 to help assess how your body is handling thyroid hormone. It is usually interpreted with T3, T4, and thyroid-stimulating hormone (TSH), rather than used by itself to diagnose a thyroid disorder.

How is the test performed?

A blood sample is collected, and the serum or plasma is separated for laboratory analysis. The laboratory then measures rT3 using HPLC and reports the result to your clinician.

How do I prepare for the test?

Fasting is generally not required for this test, but your clinician or laboratory may have specific instructions. Do not stop thyroid medication or other medicines unless your healthcare professional tells you to do so.

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

Reverse T3 (rT3), Serum/Plasma

Frequently asked questions

What does reverse T3 measure?
This test measures rT3, a relatively inactive form of thyroid hormone. It provides information about thyroid hormone metabolism and is usually considered alongside TSH, T4, and T3.
Is fasting required for a reverse T3 test?
Fasting is usually not required, although fasting or illness can affect the result. Follow any preparation instructions from your clinician or laboratory.
Can I use a reverse T3 result to diagnose a thyroid disorder?
A result by itself generally cannot establish a thyroid disorder. Your clinician will interpret it with other thyroid tests, your symptoms, medications, 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