I Decreased erythrocyte or hemoglobin production A Nutritional deficiencies Iron deficiency Folic acid and vitamin B12 deficiency or associated metabolic abnormalities B Aplastic or hypoplastic anemias Diamond–Blackfan anemia Fanconi anemia Aplastic anemia a Transient erythroblastopenia of childhood Malignancy: leukemia, lymphoma, neuroblastoma a C Abnormal heme and hemoglobin synthesis Anemia of chronic disease Lead poisoning a Sideroblastic anemias Thalassemias II Increased erythrocyte destruction A Erythrocyte membrane defects: hereditary spherocytosis, elliptocytosis, stomatocytosis, pyknocytosis, paroxysmal nocturnal hemoglobinuria B Erythrocyte enzyme defects Defects of hexose monophosphate shunt: G6PD deficiency most common Defects of Embden–Meyerhof pathway: pyruvate kinase deficiency most common C Hemoglobinopathies Sickle cell syndromes a Unstable hemoglobins D Immune hemolytic anemia Autoimmune hemolytic anemia a Isoimmune hemolytic anemia a Infection a Viral: mononucleosis, influenzas, coxsackievirus, measles, varicella, cytomegalovirus