Chapter 24: Hemolytic Anemia Resulting from Warm-Reacting Antibodies

INTRODUCTION

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

• AHA may be classified by whether an underlying disease is present (secondary) or not (primary or idiopathic) (Table 24–1).

• AHA may also be classified by the nature of the antibody (Table 24–2).

• "Warm-reacting" antibodies are usually of the IgG type, have optimal activity at 37°C, and bind complement.

• "Cold-reacting" antibodies show affinity at lower temperatures (see Chap. 25).

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

• Warm antibody AHA is the most common type.

ETIOLOGY AND PATHOGENESIS

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

• In primary AHA, the autoantibody often is specific for a single RBC 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 (e.g., α-methyldopa) can induce specific antibodies in otherwise normal individuals by some unknown mechanism. These subside 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 few develop AHA.

• RBC autoantibodies in AHA are pathogenic.

• RBCs that lack the targeted antigen have a normal survival.

• Transplacental passage of autoantibodies to a fetus ...