EPO and anemia (phenotype): The causes of anemia in humans can be classified into four major categories: (i) hematopoietic disorders in the bone marrow (e.g., decreased erythropoietin production and response, myelogenous leukemia), (ii) increased erythrocyte destruction (e.g., increased vulnerability of RBCs, immune abnormalities attacking normal RBCs, increased splenic function), (iii) bleeding (e.g., trauma, gastrointestinal bleeding), and (iv) secondary anemia (e.g., impaired iron utilization, chronic inflammation, malignancy tumors, renal dysfunction).