Chapter 16: Hemolytic Anemias

CHAPTER 16: Hemolytic Anemias

KEY TERMS

• Acquired hemolytic anemia: A type of anemia caused by conditions outside the red blood cell that leads to its destruction.
• Autoimmune hemolytic anemia: A condition where the immune system produces antibodies against one's own red blood cells, leading to their destruction.
• Complement: A system of proteins in the blood that helps antibodies kill bacteria and also plays a role in hemolytic anemia.
• Extravascular hemolysis: Destruction of red blood cells occurring primarily in the spleen or liver.
• Intrinsic hemolytic anemia: A type of hemolytic anemia due to defects within the red blood cell, such as membrane defects or enzyme deficiencies.
• Extrinsic hemolytic anemias: Hemolytic anemias caused by external factors, such as autoimmune reactions or infections.
• Glucose-6-phosphate dehydrogenase (G6PD): An enzyme that protects red blood cells from oxidative damage; its deficiency can lead to hemolytic anemia.
• Hemoglobinuria: The presence of hemoglobin in the urine, which can occur after hemolysis.
• Hemolytic anemias: Anemia resulting from the destruction of red blood cells.
• Intravascular hemolysis: Destruction of red blood cells occurring within the bloodstream.
• Isoimmune hemolytic anemia: Hemolytic anemia occurring due to the transfer of antibodies from one individual to another, such as from mother to fetus.
• Methemoglobin reductase deficiency: A rare genetic disorder that leads to the accumulation of methemoglobin, impairing oxygen delivery.
• Paroxysmal cold hemoglobinuria: A form of anemia characterized by hemolysis occurring when blood is exposed to cold temperatures.
• Paroxysmal nocturnal hemoglobinuria: A rare acquired disorder that causes intravascular hemolysis and associated symptoms.
• Pyruvate kinase deficiency: A hereditary condition leading to hemolytic anemia due to insufficient pyruvate kinase enzyme.

LEARNING OUTCOMES

Hemolytic anemias

• Definition: Hemolytic anemia is defined as a condition marked by the premature destruction of erythrocytes (red blood cells), resulting in a decreased lifespan of these cells and subsequent anemia.
• Categories of hemolytic anemia:
  • Three categories of intrinsic versus extrinsic hemolytic anemia:
  1. Causes - Intrinsic defects (e.g., membrane defects, hemoglobin abnormalities) vs. extrinsic factors (e.g., immune responses, infections).
  2. Inheritance - Inherited (genetic) versus acquired conditions.
  3. Location of hemolysis - Intravascular (within blood vessels) vs. extravascular (spleen or liver).

The role of complement in hemolytic anemia

• Describing complement action: The complement system is a series of proteins that help antibodies kill pathogens and can also mediate hemolysis through various pathways:
  1. Classical pathway: Triggered by IgG or IgM antibodies.
  2. Mannose-binding lectin pathway: Activated by carbohydrates on pathogens.
  3. Alternative pathway: Constitutively activated; plays a significant role in innate immunity.
  4. Additional pathways: Thrombin and other proteases that can initiate complement activation.
• Mechanism of action: All pathways activate a central component, C3, leading to the formation of the membrane attack complex (MAC) and hemolysis of antibody-coated cells.

Inherited hemolytic anemias

• Categories of inherited disorders:
  1. Structural membrane defects: Includes hereditary spherocytosis, elliptocytosis, stomatocytosis, and xerocytosis.
  2. Erythrocytic enzyme defects: Including G6PD deficiency, pyruvate kinase deficiency, and methemoglobin reductase deficiency.
  3. Defects of hemoglobin molecules: Such as sickle cell anemia and thalassemia.
• Membrane defects: Membrane integrity, flexibility, and surface area-to-volume ratio influence red blood cell lifespan.
  • Structural proteins affected include spectrin, band 3, and other cytoskeletal components, which can lead to instability and premature destruction of red blood cells.

Acquired hemolytic anemias

• Categories:
  1. Immune-mediated hemolytic anemias: Related to autoantibodies or isoantibodies.
  2. Drug-induced hemolytic anemias: Resulting from specific drugs or substances that affect red blood cell survival.
  3. Infections: Certain bacterias and viruses can cause hemolysis.
  4. Physical and chemical agents: Lead, extreme heat, or physical trauma can lead to hemolytic anemia.
• Mechanisms of drug-induced hemolytic anemia: Can involve direct red cell damage or immune-mediated reactions resulting from antibodies formed in response to drugs.

Complement-mediated disease

• Paroxysmal nocturnal hemoglobinuria (PNH): Caused by mutations leading to deficiency of GPI, rendering red blood cells susceptible to complement-mediated hemolysis.
• Clinical signs and symptoms: Include fatigue, hemoglobinuria, and thrombosis.
• Diagnosis: High-sensitivity flow cytometry detecting deficient GPI-anchored proteins.

Case studies

• Analyze clinical indicators, such as blood tests, patient history, and symptoms, for diagnosing various types of hemolytic anemia:

1. Case Study 1: Indicators of spherocytosis; require reticulocyte count and osmotic fragility results.
2. Case Study 2: Cold agglutinin hemolysis indicated through blood smear and positive AHG tests.
3. Case Study 3: Hemolytic disease in a newborn due to maternal antibodies against fetal red blood cells.
4. Case Study 4: Increasing fatigue and potential hemolytic anemia indicated through CBC, urinalysis results, and signs of hemolysis.

Review Questions

• Multiple choice questions covering definitions and characteristics of hemolytic anemias related to their diagnosis, causes, and types, focusing on specific signs like spherocytosis, reticulocytosis, and enzyme deficiencies. This includes practical scenarios applicable in labs or clinical evaluations.

BIBLIOGRAPHY

• References several important journals and studies to support and guide further understanding of the mechanisms and clinical implications of hemolytic anemias, such as those seen in genetics, clinical pathology, and treatment options.