How quickly does blood reproduce?

Hormones secreted by the body stimulate the bone marrow to produce red blood cells. People on hemodialysis(due to kidney failure) with a low blood count take a synthetic(man- made) hormone called Epogen or Procrit to help stimulate blood cell production. It's very expensive, but since it came into use, it drastically reduced the need for blood transfusions in the dialysis clinic. A healthy person can produce enough hormone to stimulate red blood cell production & replace the blood lost, unless it's massive volume. I