I give blood every eight weeks because my RBCs and Hemoglobin were getting to the very top of range. I had a Specialist have me stop my HRT injections and draw blood and retest after 4 weeks, my levels came back to normal. I started back on and have given blood every 8-10 weeks since and gave blood 3 weeks ago and my RBC was 48, scale is 44-56 I believe. I inject 1/2 cc every four days. Hope that helps a little.....