RBCs

• What are the functions of RBCs?

  • Transport oxygen to tissues

  • Remove carbon dioxide from the tissues

  • Buffer blood pH since they contain carbonic anhydrase

• How are RBCs produced?

  • Through hematopoiesis: a two-stage process involving…

    • Mitotic division (proliferation)

    • Maturation (differentiation)

• What is the role of erythropoietin?

  • Hormone from kidney that stimulates erythrocyte production

• Where does RBC destruction occur?

  • 80-90% of RBCs get digested by macrophages in spleen and liver

  • 10-20% of RBCs are destructed inside blood vessels

• What is the mechanism for RBC destruction?

  • As RBCs age, enzyme activities decrease and amount of membrane lipids decrease

  • The cell loses its ability to deform and becomes fragile

  • HbA levels increase

  • Heme is reduced to bilirubin

  • Globin and iron portions are conserved and reused

  • Bilirubin is then degraded to the urobilinogen and excreted primarily in the feces and urine

• What is the product of RBC destruction?

  • Bilirubin

RBC Disorders

• What are the basic etiologic classifications for anemia?

  • Under production of RBC

  • Overproduction of RBC (hemolysis)

  • Blood loss

Aplastic Anemia

• What is aplastic anemia?

  • Stem cell disorder characterized by reduction of hematopoietic tissue, fatty marrow replacement

• What is the pathogenesis of aplastic anemia?

  • Caused by toxic, radiant, or immunological injury to the bone marrow stem cells

• What is pancytopenia?

  • Low RBC, WBC, and platelets

What are the laboratory features of aplastic anemia?

• Pancytopenia

• Low WBC is important for prognosis (low leukocytes = susceptibility

Pernicious Anemia

• Folate deficiencies are associated with neural tube defects

• Pernicious anemia is characterized by the lack of intrinsic factor, resulting in the inability to absorb vitamin B12, which plays a role in RBC formation

• What are the laboratory features of pernicious anemia?

  • Pancytopenia with increased molecular corpuscular volume (MCV); megaloblastic dysplasia

  • Macrocytic and hypersegmented neutrophils

Anemia due to Renal Failure

• What is the etiology of anemia due to renal failure?

  • Primarily from failure of the renal endocrine function, with causes impaired erythropoietin (EPO) production

  • Secondarily from failure of renal excretory function

• Anemia due to renal failure leads to hemolysis, bone marrow cell depression, and blood loss

• What are the laboratory features and clinical manifestations of anemia due to renal failure?

  • Low RBC, hematocrit, and hemoglobin

  • Some grossly deformed RBC

  • General signs and symptoms of anemia usually manifest when hematocrit decreases to <20%

Iron Deficiency Anemia

• Iron deficiency anemia is the most common form of anemia and results in the unavailability of iron for hemoglobin synthesis

• What are the laboratory features of iron deficiency anemia?

  • Smaller and paler RBCs

  • Low RBC indices: MCV, MCH, MCHC

  • Decreased serum ferritin

Thalassemia

• Thalassemia is an inherited blood disorder caused by increased RBC destruction (hemolysis), resulting in decreased RBC survival rates

• Thalassemia is associated with mutant genes that suppress the rate of globin chain synthesis

• Thalassemia is classified by the polypeptide chains with deficient synthesis

• Thalassemia major is the most clinically severe and homozygous

• Thalassemia minor is less severe and heterozygous

• What are the laboratory features of thalassemia?

  • Hypochromic, microcytic RBCs

  • MCV, MCH, and MCHC are low

  • Erythroblastic hyperplasia (bone marrow)

Sickle Cell Anemia

• Sickle cell anemia is characterized by a genetically determined defect of hemoglobin synthesis, resulting in hemoglobin instability and insolubility

• Sickle cell anemia is found in hemoglobin S, in which a single amino acid substitution causes the structural abnormality

• Sickled cells cause vascular occlusion

• What are the laboratory features of sickle cell anemia?

  • Sickled RBCs present in blood smear

Polycythemia

• Polycythemia is characterized by excess RBCs, which results in increased blood viscosity, leading to clinical symptoms, such as hypertension

• Primary polycythemia is characterized by

  • An absolute increase in RBC mass, leukocytosis, and thrombocytosis

  • Increased uric acid because of excess proliferation

  • Oxygen saturation is normal

• The signs and symptoms of increased viscosity of blood are:

  • Hypertension

  • Thrombosis

  • Congested spleen and liver

• Secondary polycythemia is characterized by increased RBC production WITHOUT an increase in WBCs or platelets