EPO and anemia (phenotype): Anemia of prematurity (AOP), defined by the development of anemia with an onset that occurs after 6 weeks of life, is characterized as a normocytic, normochromic, hypoproliferative anemia, associated with several postnatal risk factors and conditions, including decreased serum hemoglobin (Hb), hematocrit (HCT), and erythropoietin (EPO) levels, reduced red blood cell (RBC) production and survival, hemorrhage, hypovolemia, and hemolysis [28,29,30].