T3 Uptake
An indirect measure of available thyroid hormone binding sites, used to interpret total T4.
| Typical reference range | 22–35 % |
Ranges vary by laboratory, method, age and sex: always use the range printed on your own report. Why labs differ.
What it measures
Despite its name, T3 uptake does not measure T3 in the patient. It estimates unoccupied binding sites on thyroid-binding proteins, which helps correct total T4 for binding-protein changes (Free T4 Index = total T4 x T3 uptake / 100).
Why it matters
It is a legacy test that, combined with total T4, approximates free T4 status. Direct free T4 measurement has largely replaced it.
What a high result can mean
High values occur with hyperthyroidism or reduced binding proteins (androgens, nephrotic syndrome, liver disease).
What a low result can mean
Low values occur with hypothyroidism or increased binding proteins (pregnancy, estrogen).
What affects the result
Only meaningful alongside total T4.
Unit
Usually reported in %.
Also called on lab reports
T3 Resin Uptake, T3U, T-Uptake
Related tests: Thyroid
This page is educational and does not replace advice from a healthcare professional.