Introduction Increase in RBC without megaloblasts present in the bone marrow Associated with accelerated erythropoiesis Caused by liver disease alcoholism folate/B12 may be normal metabolic disorder congenital deficiencies of purine or pyrimidine synthesis hypothyroidism, COPD hemolytic anemia aplastic anemia MDS Reticulocytosis may increase MCV reticulocytes are bigger than mature RBCs