Haptoglobin main function is to form a stable complex, and then combined with the free hemoglobin mononuclear - macrophage system disposed. Under normal circumstances, the human red blood cells in the circulating blood, despite continuing subject to mechanical damage, but still maintain its integrity, with the erythrocytes having a good plasticity of the cell morphology and blood micro-environment is relatively stable. Some reason induced red blood cells in the blood vessel destruction, a large number of hemoglobin released into the blood circulation, the hemoglobin from human kidney filtration, cause kidney damage, and even cause irreversible renal damage. Haptoglobin and free hemoglobin combine to form a stable complex, due to its large molecular size, can not be excreted from the kidney, which can prevent the hemoglobin from glomerular filtration to avoid the damage of free hemoglobin in the renal tubules.