T3 Uptake (T3 Resin Uptake)
Produced by: Not Applicable
Definition / Purpose: T3 uptake is an indirect measure of the quantity of thyroxine binding proteins (thyroid binding prealbumin, albumin, and TBG) in the blood. It is directly proportional to the degree of saturation of the binding proteins by thyroxine.
Why it is worthless: It is indirectly measuring the amount of T3 but does not quantify free T3 vs. bound and inactive T3. T3 Uptake is also influenced by sex hormone levels. If testosterone levels are high, T3 Uptake will be high. If Estrogen levels are high, T3 uptake will be low.
Lab Reference Range: Who cares?
When to order: Never
Pearls: Order a different test. It’s not going to help.