EXTRINSIC IMMUNE

• MCHC


  Mean corpuscular hemoglobin concentration
• RDW


  Red cell distribution width
• PLT


  Platelet count
• Reticulocytes


  Immature red blood cells
• Neutrophils


  Type of white blood cell
• Bands


  Immature neutrophils
• The ECG was normal
• The blood cell analyzer printout flagged for nucleated red blood cells (and corrected the WBC for them), 3+ anisocytosis, and reticulocytosis
• The urinalysis report included 2+ protein, 2+ blood, and increased urobilinogen, with 0 to 5 RBCs seen on microscopic examination
• Patient's serum was moderately icteric, and total serum bilirubin was increased
• Serum haptoglobin was decreased, serum indirect (unconjugated) bilirubin and lactate dehydrogenase (LD) were elevated, and urine hemosiderin was positive
• Antibody screen


  Negative at the immediate spin and 37° C incubation phase but showed 3+ agglutination in the antihuman globulin (AHG) phase for all panel cells and the autocontrol
• Direct antiglobulin test (DAT)


  Showed 3+ agglutination with polyspecific AHG and monospecific anti-IgG but was negative with monospecific anti-C3b/C3d (complement)
• Acid elution


  Performed on the patient's RBCs, and the eluate showed 2+ reactions with all panel cells and autocontrol at the AHG phase
• The patient was continued on prednisone for 4 months with slowly decreasing levels of the drug
• The patient also received bisphosphonates, vitamin D, and calcium to prevent osteoporosis, an adverse effect of prednisone
• At 3 weeks postdiagnosis, spherocytes were no longer present on the peripheral blood film, urinalysis was normal, and the DAT was negative
• Immune hemolytic anemia and nonimmune hemolytic anemia are two broad categories comprising the extrinsic hemolytic anemias
• Immune hemolytic anemias are conditions in which RBC survival is shortened as a result of an antibody-mediated mechanism
• Immune hemolytic anemias may be classified into the following groups

  • Autoimmune hemolytic anemia
  • Alloimmune hemolytic anemia
  • Drug-induced immune hemolytic anemia
• IgG


  Immunoglobulin G, a monomer in a Y-like structure with two identical heavy chains and two identical light chains connected by disulfide bonds
• IgM


  Immunoglobulin M, a pentamer consisting of five monomeric units connected by disulfide linkages
• Classical complement pathway


  1. C1 (Clq, Clr, Cls) binds to adjacent antibody Fc domains to activate the pathway

  2. C4 and C2 are cleaved, resulting in the binding of C4bC2a complexes to the RBC membrane

  3. C4bC2aC3b (C5 convertase) converts C5 to C5b, which combines with C6, C7, C8, and multiple C9s to form the membrane attack complex (MAC)
• Hemolysis mediated by IgM antibodies requires complement and can result in both extravascular and intravascular hemolysis
• Hemolysis mediated by IgG antibodies occurs with or without complement and predominantly by extravascular mechanisms
• IgG-sensitized RBCs are only partially phagocytized by macrophages, which results in removal of some membrane, leading to the formation of spherocytes
• Laboratory findings in immune hemolytic anemia include decreased hemoglobin; increased reticulocyte count; increased levels of indirect serum bilirubin and lactate dehydrogenase; and decreased serum haptoglobin level
• The direct antiglobulin test (DAT) detects in vivo sensitization of the RBC surface by IgG, C3b, or C3d
• Intravascular hemolysis


  Severe, haptoglobin level moderately to severely decreased, plasma hemoglobin increased, patient may have hemoglobinuria or hemosiderinuria
• Mean cell volume (MCV)


  May be increased because of reticulocytosis and RBC agglutination
• Findings on peripheral blood film

  • Polychromasia (reticulocytosis), spherocytes (IgG-mediated membrane damage), RBC agglutination, nucleated RBCs, fragmented RBCs or schistocytes, erythrophagocytosis
• To determine if hemolysis is due to immune mechanism

  1. Perform direct antiglobulin test (DAT)

  2. Polyspecific antihuman globulin (AHG) added to saline-washed patient RBCs

  3. Agglutination indicates RBC sensitization by IgG, C3b, or C3d

  4. If DAT positive, test with monospecific anti-IgG and anti-C3b/C3d

  5. Identify type of sensitization
• Identify specificity of IgG antibody

  1. Perform indirect antiglobulin test (IAT)

  2. Assess reaction of eluate with screening and panel reagent RBCs

  3. Identify any circulating alloantibodies or autoantibodies
• DAT may be negative in some immune hemolytic anemias
• Other disorders besides immune hemolytic anemia can cause a positive DAT
• Autoimmune hemolytic anemia (AIHA)

  Rare disorder characterized by premature RBC destruction and anemia caused by autoantibodies that bind to RBC surface with or without complement activation
• Autoimmune hemolytic anemias


  • Warm autoimmune hemolytic anemia
  • Cold agglutinin disease
  • Paroxysmal cold hemoglobinuria
  • Mixed-type AIHA
• Warm autoimmune hemolytic anemia (WAIHA)


  Most common autoimmune hemolytic anemia, 70-80% of cases
• WAIHA


  Autoantibodies react optimally at 37°C, majority are IgG
• Conditions associated with secondary WAIHA

  • Lymphoproliferative diseases
  • Nonlymphoid neoplasms
  • Autoimmune disorders
  • Immunodeficiency disorders
  • Viral infections