I. Conditions which result in significant intravascular hemolysis

  1. Paroxysmal nocturnal hemoglobinuria (PNH)
    1. An acquired clonal disorder of hemopoietic stem cells, involving inability of complement proteins to attach to the erythrocyte, rendering them extremely sensitive to complement-mediated lysis
    2. Results in chronic intravascular hemolysis
    3. Characterized by episodes of severe intravascular hemolysis, with hemoglobinuria (sometimes to the point of the urine turning black), dysphagia, abdominal pain, erectile dysfunction, thrombosis, disabling fatigue, and in severe cases, renal failure
    4. Paroxysms can be triggered by infection, drugs, or trauma; some seem to occur spontaneously; usually last 3-7d
  2. Sickle Cell Disease
  3. Thalassemias
  4. Hereditary spherocytosis
  5. Thrombotic Thrombocytopenic Purpura and other microangiopathic hemolytic anemias
  6. Pyruvate kinase deficiency
  7. Glucose-6-phosphate dehydrogenase deficiency
  8. Transfusion reactions due to ABO mismatch
  9. Paroxysmal cold hemoglobinuria
  10. Severe idiopathic autoimmune hemolytic anemia
  11. Infection-induced anemia
  12. Malaria
  13. Cardiopulmonary bypass
  14. Mechanical heart valve-induced anemia
  15. Chemical-induced anemias
  16. Autoimmune hemolytic anemia
    1. Rare; slight female predominance; peak incidence in 7th decade of life
    2. Characterized by auto-antibodies or complement coating erythrocytes, leading to phagocytosis by macrophages
    3. Presentation
      1. Onset is often rapid resulting in presentation with severe symptoms due to anemia (extreme weakness, dyspnea, tachycardia, and cardiovascular instability)
      2. Insidious onset is also possible, with jaundice and dark urine
      3. Diagnosis requires evidence of hemolysis (see below) with elevated reticulocyte count, and evidence of either RBC auto-antibodies or complement C3d on Coombs' testing
      4. Can cause venous thromboembolism (10-30% of cases)
    4. Two categories-IgG and IgM
    5. IgG ("warm antibody-mediated AIHA")
      1. 50-75% of cases
      2. Peripheral blood smear shows spherocytosis w/o RBC fragmentation
      3. Direct Coombs' test is positive in 99% of cases
      4. 35-40% have a diagnosable underlying disease e.g. SLE or other autoimmune disorders, lymphoproliferative malignancies (e.g. CLL and Hodgkin's), autoimmune hepatitis, or history of organ transplant
    6. IgM ("cold agglutinin-mediated AIHA")
      1. 15-30% of cases
      2. Involves IgM antibodies that bind to RBCs at cold temperatures only
      3. Symptoms include acrocyanosis and fatigue, often brought on by cold exposure
      4. Peripheral blood smear shows RBC clumping (MCV can be very high due to erroneous automated measurements)
      5. Direct Coombs' test is often positive for complement only, since the IgM cold agglutinin antibodies wash off RBC membrane, but C3 complement remains on the RBC surface
      6. In elderly, usually associated with indolent beta cell lymphoproliferative disorders (with a monoclonal IgM Ab that binds to RBC membranes at reduced temperatures)
      7. In young patients, often associated with mycoplasma or Epstein-Barr virus infection
      8. IgM cold aggluitin titers usually > 1:1,000
    7. Drug-associated AIHA
      1. 12-18% of cases
      2. Drugs include cefotetan (most common), ceftriaxone, penicillins, piperacillin/taxobactam, hydrochlorothiazide, acetaminophen, sulfonamides, insulin, and diclofenac
    8. Management
      1. Transfusion as appropriate for severe anemia
      2. For "warm" antibody-mediated AIHA, usually prednisone 1mg/kg/d until HCT > 30% then taper; if no improvement within 3wks, often a 2nd-line therapy is added (splenectomy or tx with rituximab, a monoclonal anti-CD20 antibody that depletes B lymphocytes so they can't produce as many autoantibodies; then search for accessory spleen or  cyclophosphamide, azathioprine, cyclosporine, or mycophenolate)
      3. For "cold" antibody-mediated AIHA, avoidance of cold and chemotherapy for lymphoma if appropriate (doesn't respond to splenectomy or steroids)

II. Diagnosis of hemolysis

  1. Serum LDH usually elevated in proportion to severity of hemolysis
  2. Also elevated indirect bilirubin, low serum haptoglobin, and hemoglobinuria are present
  3. Peripheral blood smear often shows spherocytes and other RBC changes
  4. Coombs' testing
    1. aka "antiglobulin test"
    2. Actually there are two different "Coombs' tests", "direct" and "indirect"
    3. Direct Coombs' test (aka "direct antiglobulin test")
      1. More commonly used than indirect
      2. Tests for autoimmune hemolytic anemia
      3. Detects RBCs with IgG bound to their surface and/or complement proteins bound to the IgG antibodies
      4. Patient's blood is taken and their RBCs "washed" (to remove patient's plasma), then incubated with "Coombs reagent" (antibodies against human IgG and IgM); If RBCs agglutinate, that is a positive result, indicating that the patient's RBCs have antibodies and/or complement bound to them.
    4. Indirect Coombs' test (aka "indirect antiglobulin test")
      1. Used primarily for pregnant women and patients prior to a blood transfusion
      2. Detects free antibodies in patient's serum
      3. Patient's serum is incubated with foreign RBCs; if RBCs agglutinate, that is a positive result, indicating that the patient has anti-RBC antibodies

III. Physiologic sequelae of intravascular hemolysis

  1. Nitric oxide has a paracrine function; secreted by endothelium and acting to relax vascular smooth muscle
  2. Hemoglobin reacts rapidly and irreversibly with nitric oxide, depleting intravascular nitric oxide
  3. Natural mechanisms scavenge the small amount of intravascular free hemoglobin produced by physiologic hemolysis
  4. Pathologic hemolysis overwhelms these mechanisms, resulting in accumulation of cell-free intravascular hemoglobin and reducing nitric oxide concentrations

IV. Clinical manifestations of hemolysis

  1. Smooth muscle dystonias (due to nitric oxide deficiency), including:
    1. Arterial hypertension (due to vasoconstriction)
    2. Gastrointestinal contractions (resulting in abdominal pain and dysphagia)
    3. Erectile dysfunction
  2. Abnormal thrombosis (due to nitric oxide deficiency increasing platelet activation)

(Sources include JAMA 293:1653, 2005 and (Sources include Core Content Review of Family Medicine, 2012)