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INTRODUCTION

  • In autoimmune hemolytic anemia (AHA), shortened red cell survival is the result of host antibodies that react with autologous red cells.

  • AHA may be classified by whether an underlying disease is present (secondary) or not (primary or idiopathic) (Table 22–1).

  • AHA may also be classified by the nature of the antibody (Table 22–2).

  • “Warm-reacting” antibodies are usually of the immunoglobulin G (IgG) type, have optimal activity at 37°C, and bind complement.

  • “Cold-reacting” antibodies show affinity at lower temperatures (see Chap. 23).

  • Occasionally, mixed disorders occur with both warm and cold antibodies.

  • Warm-antibody AHA is the most common type.

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TABLE 22−1 CLASSIFICATION OF WARM-ANTIBODY−MEDIATED AUTOIMMUNE HEMOLYTIC ANEMIA (AHA)
  1. On basis of presence or absence of underlying or significantly associated disorder

    1. Primary or idiopathic AHA (no apparent underlying disease)

    2. Secondary AHA

      1. Associated with lymphoproliferative disorders (eg, Hodgkin or non-Hodgkin lymphoma)

      2. Associated with the rheumatic disorders, particularly systemic lupus erythematosus

      3. Associated with certain infections (eg, Mycoplasma pneumoniae)

      4. Associated with certain nonlymphoid neoplasms (eg, ovarian tumors)

      5. Associated with certain chronic inflammatory diseases (eg, ulcerative colitis)

      6. Associated with ingestion of certain drugs (eg, α-methyldopa)

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TABLE 22−2 MAJOR REACTION PATTERNS OF THE DIRECT ANTIGLOBULIN TEST AND ASSOCIATED TYPES OF IMMUNE INJURY
Reaction Pattern Type of Immune Injury
IgG alone

Warm-antibody autoimmune hemolytic anemia

Drug-immune hemolytic anemia: hapten drug adsorption type or autoantibody type

Complement alone

Warm-antibody autoimmune hemolytic anemia with subthreshold IgG deposition

Cold-agglutinin disease

Paroxysmal cold hemoglobinuria

Drug-immune hemolytic anemia: ternary complex type

IgG plus complement

Warm-antibody autoimmune hemolytic anemia

Drug-immune hemolytic anemia: autoantibody type (rare)

ETIOLOGY AND PATHOGENESIS

  • AHA occurs in all age groups, but the incidence rises with age, in part because the frequency of lymphoproliferative malignancies increases with age.

  • In primary AHA, the autoantibody often is specific for a single red cell membrane protein, suggesting that an aberrant immune response has occurred to an autoantigen or a similar immunogen; a generalized defect in immune regulation is not seen.

  • In secondary AHA, the autoantibody most likely develops from an immunoregulatory defect.

  • Certain drugs (eg, α-methyldopa) can induce specific antibodies in otherwise normal individuals by an unknown mechanism. These antibodies decrease and disappear spontaneously when the drug is stopped.

  • The red cells of some apparently normal individuals may be found coated with warm-reacting autoantibodies similar to those of patients with AHA. Such antibodies are noted in otherwise normal blood donors at a frequency of 1 in 10,000. A very few subsequently develop AHA.

  • Red cell autoantibodies in AHA are pathogenic.

  • Red cells that lack the targeted antigen have a normal survival in the presence of the antibody.

  • Transplacental passage of autoantibodies to a fetus can cause hemolytic anemia.

  • Antibody-coated red cells are trapped by macrophages primarily in the spleen, where they are ingested and destroyed or partially ...

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