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Thyroxine (T4) Uptake, Serum/Plasma

Published: August 9, 2026Updated: August 16, 2026

A blood test that estimates how strongly thyroid hormones bind to blood proteins, providing indirect information about thyroid function.

Quick summary

["T4 uptake is an indirect thyroid test used mainly alongside other thyroid measurements."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
74793-1
Short code
T-uptake NFr SerPl
Synonyms
T-uptake NFr SerPl
Category
thyroid
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
0.8
Ref high
1.2
Critical range
— – 5 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
85610
SNOMED
396252006
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?

T4 uptake, also called a thyroid uptake test, estimates the body’s capacity to bind thyroid hormones to proteins in the blood. It is generally used as an indirect measure of thyroid function and is usually interpreted with other thyroid tests.

Why might I need this test?

This test may be ordered to help evaluate suspected thyroid disease or unexplained symptoms such as fatigue, weight changes, heat intolerance, or cold intolerance. It may also help assess how thyroid-hormone binding is affected by medications, pregnancy, or nonthyroid illnesses.

How is the test performed?

A blood sample is collected, and the serum or plasma is analyzed using a validated laboratory method. Historically, some T4 uptake tests used a radioactive tracer and a resin, but many current laboratories use other methods.

How do I prepare for the test?

No special preparation is usually required for a routine blood draw. Tell your clinician about thyroid medicines, iodine or contrast products, pregnancy, and recent illness because these can affect thyroid test results.

Reference range

INR: 0.8-1.2 (warfarin: 2.0-3.0)N/A

Specimen: serum

Inform your healthcare provider if you are taking blood thinners. No special preparation required.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

T4 uptake test

Frequently asked questions

Is T4 uptake the same as a thyroid scan?
No. A thyroid scan uses radioactive material to create images of the thyroid’s uptake of iodine. T4 uptake is a blood test that estimates thyroid-hormone binding capacity.
Is fasting required for a T4 uptake test?
Usually not. Follow any fasting instructions provided by the ordering clinician or laboratory, especially if additional thyroid tests are being performed.
Why is T4 uptake rarely used by itself?
It provides indirect information and can be affected by medications, pregnancy, and other illnesses. Direct thyroid measurements such as free T4 and thyroid-stimulating hormone are often more useful for current evaluation.
  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 16, 2026. · Read our editorial policy