What is the reference range for T3U?

What is the reference range for T3U?

• A. 15-25%
• B. 25-38%
• C. 40-60%
• D. 50-70%

Answer: (B)

Understanding the reference range for T3U helps you interpret how much binding capacity is available for thyroid hormones on transport proteins. T3U, or T3 uptake, is a historical measure that reflects the binding sites available on thyroid hormone transporters, mainly thyroxine-binding globulin (TBG). It is inversely related to TBG levels: when TBG is high, T3U is low; when TBG is low, T3U is high. The typical reference range cited in many labs is about 25–38%. This range corresponds to normal TBG levels and normal thyroid physiology. The other ranges listed are outside the usual interval and would not represent a normal, euthyroid state. In practice, T3U is rarely used alone today but was historically paired with another thyroid test to estimate the Free Thyroxine Index.

Understanding the reference range for T3U helps you interpret how much binding capacity is available for thyroid hormones on transport proteins. T3U, or T3 uptake, is a historical measure that reflects the binding sites available on thyroid hormone transporters, mainly thyroxine-binding globulin (TBG). It is inversely related to TBG levels: when TBG is high, T3U is low; when TBG is low, T3U is high. The typical reference range cited in many labs is about 25–38%. This range corresponds to normal TBG levels and normal thyroid physiology. The other ranges listed are outside the usual interval and would not represent a normal, euthyroid state. In practice, T3U is rarely used alone today but was historically paired with another thyroid test to estimate the Free Thyroxine Index.