Approximately what percentage of testosterone is bound to albumin?

• A. 50%
• B. 25%
• C. 75%
• D. 10%

Answer: (A)

Testosterone in the bloodstream is largely protein-bound. SHBG binds a substantial portion with high affinity, while albumin binds with lower affinity but high capacity, providing a large reservoir. The free fraction is small, typically around 1–2%. Because of these binding dynamics, about half of circulating testosterone is bound to albumin, with the remainder mainly bound to SHBG (and a tiny amount free). That makes 50% the best approximation.

The other options are outside the typical distribution: 75% would imply more albumin binding than is usually observed, 25% underestimates the albumin-bound pool, and 10% is too low for the albumin portion.