Which plasma protein binds free hemoglobin?

Haptoglobin is the plasma protein that specifically binds to free hemoglobin in the bloodstream. When red blood cells are lysed, hemoglobin is released into the circulation. Haptoglobin plays a crucial role in this context by binding to the released hemoglobin and forming a haptoglobin-hemoglobin complex. This complex is then cleared by the liver, thereby preventing the loss of hemoglobin and iron through the kidneys and protecting the kidneys from potential damage due to free hemoglobin.

This binding mechanism is particularly important in the management of hemolytic conditions, where there is an increased breakdown of red blood cells and consequently more free hemoglobin in circulation. Haptoglobin levels can serve as a clinical indicator of hemolysis – low haptoglobin levels suggest increased hemolysis since all available haptoglobin may be bound to the excess free hemoglobin.

In summary, haptoglobin's ability to bind free hemoglobin is vital for iron recycling and protecting the body from the consequences of hemolysis, making it the correct answer to the question.