Immune-mediated acquired hemolytic anemia encompasses three main categories: autoimmune, alloimmune, and drug induced.
AUTOIMMUNE HEMOLYTIC ANEMIA
Individuals with autoimmune hemolytic anemia make antibodies against their own RBCs.1 Diagnosis requires evidence of an antibody on the patient's RBCs, usually accompanied by an autoantibody in the plasma. The direct antigen test, also known as the direct Coombs test, is performed by combining the patient's anticoagulated, washed RBCs with anti–immunoglobulin G and anti-C3d (complement) antibodies to detect the presence of immunoglobulin G and/or complement on the RBC surface. A positive direct antigen test consists of the detection of either immunoglobulin G or complement on the RBC surface; it does not require the detection of both.2 A positive direct antigen test is not specific for a diagnosis of autoimmune hemolytic anemia (Table 237-2), nor does the presence of immunoglobulin G and/or complement on a patient's RBCs indicate the severity of disease; the direct antigen test is, however, a critical confirmatory screen. The indirect Coombs test looks for the presence of autoantibodies in the patient's serum, testing against a panel of RBCs bearing specific surface antigens. Hemolysis can take place within the vascular space or extravascularly within the liver or spleen.
TABLE 237-2Differential Diagnosis of Positive Direct Antigen (Direct Coombs) Test ||Download (.pdf) TABLE 237-2 Differential Diagnosis of Positive Direct Antigen (Direct Coombs) Test
Autoimmune hemolytic anemia
Hemolytic transfusion reaction, acute or delayed
Hemolytic disease of newborn
Drug-related hemolytic anemia
IV immunoglobulin therapy
Rh(D) immunoglobulin therapy
Antilymphocyte globulin therapy
Antithymocyte globulin therapy
Sickle cell disease
Systemic lupus erythematosus
Human immunodeficiency virus/acquired immunodeficiency syndrome
Autoimmune hemolytic anemia can be divided into primary and secondary disease; primary, or idiopathic, disease occurs without a known underlying etiology, whereas secondary disease is associated with an underlying disorder.1 Primary disease is more common in women, with peak incidence during the fourth and fifth decades. Many cases initially designated as primary are later found to be associated with lymphoproliferative, autoimmune, or infectious diseases. In children, the disorder is commonly associated with viral or respiratory infections and can cause acute, fulminant hemolysis. Pregnancy can increase the risk of autoantibody development fivefold, but significant RBC destruction is not common. Autoimmune hemolytic anemia is further divided into autoantibody type: warm type, cold type, and mixed type (Table 237-3).1
TABLE 237-3Categories of Autoimmune Hemolytic Anemia (AIHA) ||Download (.pdf) TABLE 237-3 Categories of Autoimmune Hemolytic Anemia (AIHA)
|Warm antibody AIHA: Autoantibodies adhere most strongly to RBCs at 37°C (98.6°F). || |
70%–80% of AIHA cases
2:1 female predominance
50% primary (idiopathic) disease
50% secondary disease: lymphoproliferative, autoimmune disease, postinfection (transient)
Usually immunoglobulin G (IgG) autoantibody against Rh(D) antigen
Hemolysis usually extravascular
Steroid responsive: 70%–80%
|Cold antibody AIHA: Autoantibodies adhere most strongly to RBCs at 0–4°C (32–39.2°F). || |
Cold agglutinin disease: IgM autoantibody against I antigen
Primary disease: older females
Secondary disease: lymphoproliferative disorders, postinfection (transient)
Raynaud's phenomenon, livedo reticularis, vascular occlusion
Attacks precipitated by cold exposure
Rarely intravascular hemolysis
Not steroid responsive
Paroxysmal cold hemoglobinuria: IgG autoantibody against P antigen
Primary disease: rare, in adults
Secondary disease: usually in children after upper respiratory infection
Intravascular hemolysis during cold weather
Usually not steroid responsive
|Mixed-type antibody AIHA: Autoantibodies have variable temperature-dependent RBC adherence. || |
Primary disease: more common in older females
Secondary disease: lymphoproliferative and autoimmune disorders
Usually chronic course with severe exacerbations
Usually steroid responsive
Warm Antibody Autoimmune Hemolytic Anemia
Warm autoantibody–mediated hemolysis is predominantly extravascular, with antibody-coated RBCs consumed mostly by splenic macrophages and, to a lesser degree, by hepatic macrophages known as Kupffer cells. Partial phagocytosis of the original RBC membrane structure leads to the formation of the more rigid, fragmentation-prone spherocyte. Increased spherocytosis found on peripheral blood smear correlates positively with severity of extravascular hemolysis.
Autoimmune hemolytic anemia is initially treated with high-dose corticosteroids, typically oral at 1 to 2 milligrams/kg per day for 3 to 4 weeks, with improvement expected in 80% to 85% of patients but complete remission in only up to 30% of patients.3
Monoclonal antibodies (e.g., rituximab), immunosuppressive agents (e.g., azathioprine, mycophenolate mofetil, cyclosporine, cyclophosphamide), or semisynthetic androgens (e.g., danazol) can be used to decrease autoantibody production.3,4 Splenectomy removes both the main site of extravascular hemolysis in IgG-mediated disease and a major site of general autoantibody production. Splenectomy shows clinical benefit in up to 60% of patients, with potential for long-term remission or a complete cure. A serious complication of splenectomy is overwhelming postsplenectomy infection due to sepsis with encapsulated bacteria.5 Such patients should receive regular pneumococcal and meningococcal vaccinations and may benefit from daily penicillin prophylaxis.
Severe hemolysis in cases of warm antibody autoimmune hemolytic anemia may be treated with plasma exchange as a transient stabilizing measure while waiting for steroids or immunosuppressive agents to take effect. IV immunoglobulin has been used as an adjunctive treatment in children who cannot tolerate the side effects of chronic high-dose steroids or immunosuppressive agents.6
For a patient with life-threatening anemia, the goal is to transfuse allogeneic RBCs without producing potentially harmful transfusion reactions. Laboratory personnel must determine whether the patient's blood contains alloantibodies against RBC antigens, but first, autoantibodies—usually directed against more commonly occurring or higher prevalence RBC antigens, and thus typically panreactive against RBC panels—must be identified and sifted out because the presence of autoantibodies can hide the existence of alloantibodies.7 The testing process can be both labor and time intensive, sometimes requiring 6 hours or longer. Once completed, however, antigen-free, compatible RBC units can then be selected in hopes of providing safe and effective transfusion for the patient. If emergently needed, transfusion of the least incompatible units may be administered slowly and in the smallest amounts necessary with close monitoring.8
Cold Antibody Autoimmune Hemolytic Anemia
Cold autoantibodies lead to clumping or agglutination of RBCs on peripheral smear at cooler temperatures. Cold antibody autoimmune hemolytic anemia is associated with complement fixation on the RBC surface and triggering of the complement cascade. Hemolysis occurs in both the extravascular and intravascular spaces. Instead of splenic macrophages, the hepatic macrophages known as Kupffer cells are responsible for most of the extravascular RBC destruction. The two major cold antibody disorders are cold agglutinin disease and paroxysmal cold hemoglobinuria. Fifty percent of secondary cold antibody cases are associated with lymphoproliferative disorders, with underlying infection as the next leading cause.
Cold agglutinin disease is exacerbated by the cold, so more episodes of acute hemolysis are seen during winter.9 Because the peripheral circulation is typically cooler than the central circulation, secondary Raynaud's phenomenon and vascular occlusion can complicate cold agglutinin disease, leading to acrocyanosis and tissue necrosis/gangrene. Painful discoloration and mottling of the skin consistent with livedo reticularis may be seen.10 Less commonly, cold urticaria and hemorrhagic vesicles may develop.11
Primary cold agglutinin disease causes chronic, recurrent hemolysis in older adults, particularly females, with a peak incidence at age 70 years old. As with all of the idiopathic autoimmune hemolytic anemias, an associated underlying disease process may be discovered well after initial presentation of cold agglutinin disease; in particular, an occult lymphoproliferative disorder may be the source of the aberrant cold autoantibodies.
Secondary cold agglutinin disease may present after infection with Mycoplasma pneumoniae, Epstein-Barr virus, or infectious mononucleosis, adenovirus, cytomegalovirus, influenza, varicella-zoster virus, human immunodeficiency virus, Escherichia coli, Listeria monocytogenes, or Treponema pallidum. Hemolysis typically begins 2 to 3 weeks after the onset of illness, corresponding with peak antibody development against the infectious agent, and resolves about 2 to 3 weeks after resolution of the infectious illness. Many patients with Mycoplasma pneumonia and infectious mononucleosis will have measurable cold agglutinin titers, but far fewer will develop symptoms and signs of hemolytic anemia. Conversely, cold agglutinin disease associated with lymphoproliferative diseases such as chronic lymphocytic leukemia and lymphoma produces high autoantibody levels with the potential for significant hemolysis.
Agglutination of RBCs can confound an automated CBC device; the mean corpuscular volume may be falsely elevated, whereas the hemoglobin registers spuriously low. Holding the blood tube in warm hands may decrease RBC clumping for more reliable CBC results. A CBC with confusing or bizarre results should undergo peripheral smear examination. Peripheral smear findings of cold agglutinin disease include spherocytosis, anisocytosis, poikilocytosis, polychromasia, and agglutination.12 The direct antigen test demonstrates adherence of complement to patient RBCs, but cold autoantibodies are typically washed off the RBCs during the elution process and thus are not identified. Other laboratory findings correspond with those routinely seen in cases of hemolytic anemia, including findings consistent with intravascular hemolysis in some cold agglutinin disease cases (Table 237-1).
An important principle in treating cold agglutinin disease is keeping the extremities and appendages, particularly the nose and ears, warm in cold weather. Patients should take a daily folate supplement for healthy RBC production. Cold agglutinin disease is less likely to respond to steroids, with response rates as low as 35%.9 Splenectomy is less effective in treating cold agglutinin disease because splenic macrophages play a lesser role in IgM-mediated cold antibody disease. Severe hemolysis has been treated successfully with immunosuppressive agents such as chlorambucil, cyclophosphamide, interferon-α, fludarabine, or rituximab.9 Because immunoglobulin M autoantibodies have an intravascular distribution, plasmapheresis may assist by removing autoantibodies from the circulation when combined with immunosuppressive agents.
Infection-related cold antibody disease does not require immunosuppressive therapy because the hemolytic anemia is usually self-limited. RBC transfusion can be performed for patients at risk for significant cardiac or cerebrovascular ischemia, but transfused blood should be infused at 37°C (98.6°F) using a blood warmer. Transfusions should be limited as they may worsen ongoing hemolysis because most cold antibodies act against the I/i group antigens that are found on most donor RBCs. Donor complement in the transfused product also may exacerbate ongoing hemolysis.
Paroxysmal cold hemoglobinuria is caused by a biphasic hemolysin immunoglobulin G autoantibody called the Donath-Landsteiner (D-L) antibody that is directed against the P antigen system found on most RBCs.13 This potent autoantibody binds to RBCs and fixes early complement cascade proteins at low temperatures, whereas terminal complement components adhere and produce intravascular lysis of RBCs at warmer, physiologic temperatures.
Bursts of cold weather–induced intravascular hemolysis lead to bouts of dark urine or hemoglobinuria for which the disease is named. Other presenting symptoms include attacks of high fever, chills, headache, abdominal cramps, nausea and vomiting, diarrhea, and leg and back pain, all exacerbated by cold weather. Cold urticaria may develop as well as extremity paresthesias and Raynaud's phenomenon.
Primary paroxysmal cold hemoglobinuria is a rare, idiopathic, chronic condition occurring in adults, characterized by cold-induced episodes of massive hemolysis. Secondary disease occurs predominantly in children, usually seen after a preceding upper respiratory infection. Most pediatric cases are self-limited and nonrecurring, but severe cases may take weeks to resolve. With severe hemolysis, hemoglobinuria is common, and methemoglobinemia may be seen. Acute renal failure may develop as a complication. Pediatric paroxysmal cold hemoglobinuria may occur after infections with measles, mumps, Epstein-Barr virus, cytomegalovirus, varicella, adenovirus, influenza A, M. pneumoniae, Haemophilus influenzae, and E. coli. Adult patients with chronic, relapsing disease should be tested for syphilis, because cold-provoked hemolysis has been associated with tertiary or late syphilis as well as with congenital syphilis.
During an attack of paroxysmal cold hemoglobinuria, acutely low hemoglobin may be seen on CBC due to sudden, severe hemolysis. The peripheral smear may demonstrate erythrophagocytosis, the engulfment of RBCs by neutrophils.12 Presence of the biphasic D-L immunoglobulin G antibody on laboratory testing is pathognomonic. Patient serum is added to two tubes containing human type O RBCs. The first tube, the control, is incubated at 37°C (98.6°F) or physiologic temperature, whereas the second tube is incubated first at 0°C (32°F) and then at 37°C (98.6°F). The D-L test is positive if hemolysis is present in the second tube, indicating presence of the biphasic D-L antibody, while absent in the control tube.14 The direct antigen test is usually positive for complement just before or after a paroxysm but often negative in between paroxysms in patients with chronic, relapsing disease.
Patients with paroxysmal cold hemoglobinuria should be kept warm. Steroids can be considered in children with severe hemolytic anemia, but because infection-related disease tends to be self-limited, benefit is uncertain. Disease secondary to syphilis responds to effective antibiotic treatment. Splenectomy is not helpful, and plasmapheresis should be used only as a temporizing measure in life-threatening cases. RBC transfusion using a blood warmer should be limited to cases of severe hemolysis because most donor units are P antigen positive and may stimulate further production of antibodies. Rituximab can successfully treat primary paroxysmal cold hemoglobinuria in adults.15
Mixed-Type Autoimmune Hemolytic Anemia
Mixed-type autoimmune hemolytic anemia, with both warm and cold autoantibodies to RBCs, presents as primary or secondary disease, most commonly associated with lymphoproliferative and autoimmune diseases, particularly systemic lupus.1 The course of illness is usually chronic with severe exacerbations. Like the warm antibody disorder, the mixed type is usually steroid responsive, can be treated with splenectomy, and responds to immunosuppressive therapy.
ALLOIMMUNE HEMOLYTIC ANEMIA
Alloimmune hemolytic anemia requires exposure to allogeneic RBCs with subsequent alloantibody formation. In the laboratory, alloantibodies react specifically with the allogeneic RBCs that triggered their production; these antibodies do not react against a patient's own RBCs. A well-known example of this is when the Rh(D)-negative maternal immune system develops immunoglobulin G alloantibodies on exposure to Rh(D)-positive fetal RBCs. The maternal alloantibodies can then cross the placenta, leading to fetal RBC destruction in a condition known as hemolytic disease of the newborn.16 Anemia can range from mild to potentially fatal, producing intrauterine fetal death. The term hydrops fetalis has been used to describe the anasarca seen in severe cases. Transplacental or fetomaternal hemorrhage, the inciting stimulus for maternal alloantibody formation, may occur during amniocentesis, chorionic villus sampling, delivery, or abortion (threatened or otherwise) or even during external cephalic version. Administration of anti-D immunoglobulin G with any fetomaternal hemorrhage event and soon after delivery will suppress maternal alloantibody formation and prevent hemolytic disease of the newborn. Treatment of established hemolytic disease of the newborn employs intrauterine and intravascular fetal transfusion and may include plasma exchange and/or IV immunoglobulin therapy.
Most adults who develop alloimmune hemolytic anemia have a history of RBC transfusion, which sensitizes patients to allogeneic RBC antigens. A subsequent transfusion can result in immediate alloantibody production, resulting in the fever, chest and flank pain, tachypnea, tachycardia, hypotension, hemoglobinuria, and oliguria seen in the hemolytic transfusion reaction (see chapter 238, "Transfusion Therapy"). In patients with high alloantibody titers, the hemolytic reaction can be immediate. Delayed alloantibody-mediated hemolysis is possible, with hemolytic transfusion reaction symptoms presenting 3 to 7 days after transfusion (see chapter 238).
DRUG-INDUCED HEMOLYTIC ANEMIA
Drug-induced hemolytic anemia is rare, estimated at 1 in 1,000,000 patients, where drug exposure induces antibody formation leading to the destruction of RBCs.17 More than 100 drugs are known to induce autoantibody production against patient RBCs (Table 237-4).18 Drug-induced hemolytic anemia can result in either a positive or negative direct antigen test and can be difficult to distinguish from autoimmune hemolytic anemia, so a careful review of current medications is important in patients with a new hemolytic anemia.
TABLE 237-4Most Often Cited Drugs Inducing Hemolytic Anemia ||Download (.pdf) TABLE 237-4 Most Often Cited Drugs Inducing Hemolytic Anemia
Patients with severe hemolysis and anemia require hospitalization and further evaluation. In all cases, stop the offending drug immediately. In the event that medications are required for treatment of patients in the ED who have evidence of ongoing hemolysis, refrain if possible from using listed agents (Table 237-4). Steroids can be used in cases of drug-related severe hemolysis.