What medical process restores the body's ability to produce RBCs?

Erythropoiesis is the physiological process responsible for the production of red blood cells (RBCs) in the body. This process occurs primarily in the bone marrow and involves the differentiation of stem cells into erythrocytes, which then mature and are released into the bloodstream. The regulation of erythropoiesis is largely influenced by erythropoietin, a hormone produced by the kidneys in response to low oxygen levels in the blood.

In contrast, the other options serve different functions in the body's hematologic or filtration systems. Hemofiltration refers to a kidney function replacement therapy that removes waste products from the blood but does not play a role in RBC production. Transfusion is a medical procedure used to replace lost blood or blood components in a patient but does not stimulate the body to produce new RBCs. Leukopoiesis involves the generation of white blood cells, which is a separate process from erythropoiesis focused on the immune response.

Therefore, the correct answer, erythropoiesis, directly addresses the body's ability to produce red blood cells.