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Historical Assessment of T-Uptake

What did the T-uptake measure?
The T3-uptake (later versions called T-uptake methods) was the original test used to estimate the level of thyroid binding proteins. These are rarely used now that there are methods available to measure free T4 and free T3 directly. 
Other names?
  • Also known as thyroid binding capacity
Why was it ordered?
  • Provides a measure of the available thyroxine-binding sites
What has replaced it?
  • Free T4 (FT4) and free T3 (FT3) immunoassays