How long will it take my red blood count to rise again?

Red blood cells have a long life -- up to 120 days -- so rebuilding the red blood count is a long, slow process. The speed with which bone marrow makes new red blood cells is also affected by factors such as the type of treatment -- particularly the type and dosage of chemo -- and a patient's general state of health.

One thing to keep in mind is that red blood counts usually won't start dropping until a week or two after treatment and will continue to fall for several more weeks. That's because chemo doesn't kill off the red blood cells already in the bloodstream, which are mature and aren't dividing rapidly. It kills off the cells forming in the marrow, and therefore there's a delayed response that corresponds with the rate at which marrow is creating new cells. The rate of regeneration can be affected by age and overall health. Also,radiation and some medications suppress the production of red blood cells, so the rebuilding process can be much slower.