Why does hemoglobinuria occur only in intravascular hemolysis?

Free hemoglobin is released directly into plasma when RBCs lyse intravascularly. Once haptoglobin is saturated, unbound hemoglobin dimers are filtered by the kidney, appearing in urine. In extravascular hemolysis, intact RBCs are phagocytosed, so hemoglobin is not released directly into circulation.