Chapter 23: Disorders of Red Blood Cells – Causes and Symptoms

Disorders of Red Blood Cells – Causes and Symptoms comprehensively details the physiology and pathology of red blood cells (RBCs), focusing on their primary role in oxygen transport via the iron-containing hemoglobin molecule. It examines the erythrocyte lifecycle, including production (erythropoiesis) regulated by renal erythropoietin in response to hypoxia, the necessary role of iron and B vitamins (B12, folic acid) for cell maturation, and the destruction process that yields unconjugated bilirubin, which, when excessive, can cause jaundice or lead to severe consequences like kernicterus in neonates. The text extensively covers transfusion medicine, outlining the critical importance of determining ABO and Rh compatibility, defining various blood components used in therapy, and classifying severe adverse reactions such as acute hemolytic transfusion reactions (AHTR), transfusion-related acute lung injury (TRALI), and transfusion-associated circulatory overload (TACO). Anemia, defined as insufficient oxygen-carrying capacity, is categorized based on etiology: blood loss, premature destruction (hemolytic), or deficient production. Hemolytic disorders are explored through intrinsic defects like inherited hemoglobinopathies (e.g., sickle cell disease, thalassemias) and enzyme deficiencies (G6PD deficiency), as well as extrinsic causes like immune reactions. Deficient production anemias are detailed, including microcytic, hypochromic iron deficiency anemia; macrocytic megaloblastic anemias resulting from impaired DNA synthesis due to B12 or folic acid deficits, noting the unique associated neurologic symptoms of B12 deficiency; aplastic anemia, involving pancytopenia from stem cell failure; and chronic disease anemias linked to reduced erythropoietin. Conversely, polycythemia, an abnormally high RBC mass, is differentiated into primary (Polycythemia Vera, a bone marrow malignancy) and secondary (a compensatory response to chronic hypoxia), with associated risks stemming from increased blood viscosity. Finally, the chapter addresses age-related hematologic changes, including the high HbF levels and physiologic anemia observed in neonates, and the decreased RBC replacement capacity seen in older adults.