68 yr old white male. My hematocrit dropped suddenly 4 years ago, from 42 to hovering around 31. Cells are not maturing. Endoscopy, colonoscopy and bone marrow were negative. Generally healthy. Not symptomatic. Exercise regularly. Not low enough for transfusion therapy. No kidney disease. Iron is abundant. O2 saturation 97%. Is there a protocol to stimulate red cell production/maturity?