What is the free fraction percentage of T4 in plasma?

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Multiple Choice

What is the free fraction percentage of T4 in plasma?

Explanation:
Thyroxine (T4) in blood is predominantly bound to transport proteins, especially thyroxine-binding globulin, with only a very small portion remaining unbound. The biologically active form is this free T4, and its fraction is tiny—about a few hundredths of a percent of the total T4. In most standard references, the free fraction is around 0.04% of the total T4. This small free pool is what enters cells and elicits effects, while the bound fraction acts as a reservoir that helps stabilize free T4 levels. Therefore, 0.04% is the correct representation of the free fraction.

Thyroxine (T4) in blood is predominantly bound to transport proteins, especially thyroxine-binding globulin, with only a very small portion remaining unbound. The biologically active form is this free T4, and its fraction is tiny—about a few hundredths of a percent of the total T4. In most standard references, the free fraction is around 0.04% of the total T4. This small free pool is what enters cells and elicits effects, while the bound fraction acts as a reservoir that helps stabilize free T4 levels. Therefore, 0.04% is the correct representation of the free fraction.

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