Chapter 14: Red Blood Cell and Bleeding Disorders

The text systematically categorizes anemias based on their underlying mechanisms, beginning with those caused by acute or chronic blood loss, and transitioning into hemolytic anemias characterized by the premature destruction of erythrocytes. Within the hemolytic category, it thoroughly explores inherited genetic defects such as hereditary spherocytosis, which compromises the red cell membrane cytoskeleton, and glucose-6-phosphate dehydrogenase (G6PD) deficiency, an X-linked enzymopathy that renders cells susceptible to oxidative stress, leading to the formation of Heinz bodies and episodic hemolysis. The chapter also provides a deep dive into hemoglobinopathies, detailing the molecular pathophysiology of sickle cell disease—where a point mutation causes deoxygenated hemoglobin to polymerize, leading to microvascular occlusion and ischemic pain crises—and the thalassemias, which involve imbalanced alpha or beta globin chain synthesis that triggers ineffective erythropoiesis, microcytosis, and severe iron overload. Acquired hemolytic conditions are equally highlighted, including paroxysmal nocturnal hemoglobinuria (driven by acquired PIGA mutations that remove protective complement-regulating proteins), immunohemolytic anemias mediated by warm or cold autoantibodies, and microangiopathic hemolytic anemias that subject red blood cells to mechanical trauma. The discussion then shifts to anemias of diminished erythropoiesis, contrasting the macrocytic, DNA-synthesis-impaired megaloblastic anemias caused by folate or vitamin B12 deficiencies (such as autoimmune pernicious anemia) with the microcytic, hypochromic profile of iron deficiency anemia, the world's most common nutritional disorder often tied to chronic hemorrhage. This section also elucidates the anemia of chronic inflammation, where cytokine-driven hepcidin elevations trap iron within macrophages, and outlines severe bone marrow failure syndromes like aplastic anemia and myelophthisic anemia. After briefly addressing polycythemia as an abnormal elevation in red cell mass, the chapter shifts to hemorrhagic diatheses, dissecting the precise mechanisms of abnormal bleeding. It differentiates between vascular wall fragilities, quantitative platelet reductions seen in immune thrombocytopenic purpura (ITP) and drug-induced states, and qualitative platelet adhesion or aggregation defects such as Bernard-Soulier syndrome and Glanzmann thrombasthenia. The text extensively details coagulation factor deficiencies, emphasizing the high prevalence of von Willebrand disease alongside the X-linked bleeding disorders Hemophilia A and B. Furthermore, it addresses complex, systemic thrombohemorrhagic emergencies like disseminated intravascular coagulation (DIC), which results in a dangerous consumptive coagulopathy, as well as thrombotic microangiopathies including thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS). Finally, the chapter concludes by outlining the critical immunologic and infectious complications associated with blood transfusions, such as acute hemolytic reactions and transfusion-related acute lung injury (TRALI), rounding out a vital study resource for understanding systemic hematologic dysfunction.