Acquired and Congenital Hemolytic Anemia

After completing this article, the reader should be able to:Hemolytic anemia (HA) affects a substantial proportion of the pediatric population globally. Many children are hospitalized every year due to sequelae of this heterogeneous disease. Clinicians should be facile in recognizing its presentation.HA may be defined as increased destruction of red blood cells (RBCs). RBCs are cleared from the circulation via extravascular or intravascular mechanisms (Figure). HA can be caused by congenital or acquired RBC abnormalities (Table 1).Extravascular hemolysis is mediated by the reticuloendothelial system (RES) of the spleen and liver. Most HAs, such as warm autoimmune hemolytic anemia (AIHA), sickle cell disease (SCD), and hereditary spherocytosis (HS), are characterized by extravascular hemolysis. The hallmark of extravascular hemolysis is phagocytosis of erythrocytes by splenic macrophages or hepatic Kupffer cells, followed by sequestration and removal. Heme, released from free hemoglobin in the phagocytosed cells, is converted to biliverdin within the phagocyte. Biliverdin is subsequently converted to bilirubin.Intravascular hemolysis is defined as damage incurred by the RBC membrane directly within the vasculature due to shear stress, toxins, or complement-mediated lysis. Examples include mechanical valve-induced hemolysis, Shiga toxin-associated hemolytic-uremic syndrome, and cold agglutinin disease. Whereas hemoglobin clearance occurs within the macrophage in extravascular hemolysis, during intravascular hemolysis, circulating free hemoglobin is bound irreversibly to the plasma haptoglobin and cleared by the liver. If free hemoglobin exceeds the binding capacity of haptoglobin, hemoglobinemia occurs. Unbound hemoglobin dimers are reabsorbed by the proximal renal tubule until the absorptive capacity is exceeded. Free hemoglobin is subsequently excreted in the urine, which appears dark.Children may present with acute or insidious onset of pallor, fatigue, and lightheadness as a consequence of anemia. New-onset or recurrent jaundice may result from unconjugated hyperbilirubinemia. Parents may describe dark urine, which is due to hemoglobinuria from intravascular hemolysis. Acrocyanosis may occur, tachycardia and/or a flow murmur may be appreciated on physical examination, and splenomegaly may be observed due to sequestration of RBCs.Adenopathy or hepatosplenomegaly should prompt investigation for malignancy or lymphoproliferative disorders. Lymphomas, in particular, can manifest with immune cytopenias, including AIHA and immune thrombocytopenia. In these cases, additional evaluation for hyperuricemia and examination of a peripheral blood smear by a hematologist is recommended. This type of paraneoplastic autoimmunity may be accompanied by constitutional symptoms suggestive of malignancy (eg, fevers, night sweats, weight loss, and fatigue).In contrast to malignancy-associated immune hemolysis, children are typically healthy before the onset of isolated AIHA, although they may have experienced nonspecific viral symptoms or fever within several weeks of diagnosis. If the hemolytic anemia is congenital, the stigmata of chronic hemolysis may be noted, such as pigmented gallstones and related sequelae, due to excess production of bilirubin.Reticulocytosis is an important distinguishing feature of hemolysis and usually exceeds 2%, with the absolute reticulocyte count greater than 100 × 103/μL (100 × 109/L). However, transient reticulocytopenia can occur in up to 33% of patients, due to in vivo hemolysis of reticulocytes, nutritional deficiencies, concurrent parvovirus infection, toxin exposure, or underlying marrow dysfunction. (1)(2)Microspherocytes are characteristic of AIHA due to membrane changes that occur when immunoglobulins are bound to the RBC surface. Fragment forms, such as schistocytes or helmet cells, may result from toxin- or shear stress-mediated hemolysis. Polychromasia, related to the increase in circulating reticulocytes, may also be reported.Unconjugated bilirubin, lactate dehydrogenase, and aspartate aminotransferase values may be elevated. The latter two intracellular enzymes are released into the plasma with cell destruction. As the plasma carrier for free hemoglobin, haptoglobin is often decreased. However, this is not a useful marker in infants younger than age 3 months.This test identifies sickle cell and β-thalassemia variants. Blood for hemoglobin electrophoresis must be collected before transfusion because it reflects the donor hemoglobin profile if performed within 3 months posttransfusion.Once hemolysis is identified, further management is based on whether the hemolysis is antibody-mediated. The direct Coombs or antiglobulin test (DAT) is the primary method to detect in vivo coating of patient erythrocytes by autoantibodies. In the DAT, a nonspecific antihuman globulin is added to the patient's RBCs. If this antibody recognizes immunoglobulin bound to the RBC surface, as in AIHA, it binds or crosslinks other bound antibodies and agglutinates the antibody-bound RBCs. Subsequently adding antihuman antibodies for complement or immunoglobulin (Ig)G identifies the type of immunoglobulin bound to the RBC surface. Binding of anticomplement antibodies usually implies bound IgM. The specific antibody binding patterns can help to differentiate between warm-reactive (IgG) and cold-reactive (IgM) AIHA.Patient serum (rather than RBCs) is incubated with healthy donor RBCs. If RBC autoantibodies in the patient's serum bind to the donor RBCs, agglutination occurs, indicating the presence of circulating antibody. This may be performed if AIHA is suspected but the DAT result is negative.Maternal antibodies to incompatible fetal RBC antigens, such as Rhesus (Rh)D, A, or B, can cause hemolytic disease in utero. In the postnatal period, infants may exhibit mild anemia to hydrops fetalis. Before the introduction of anti-D Ig prophylaxis and intrauterine transfusions, Rh disease of the newborn was the predominant cause of neonatal AIHA, which is associated with 50% mortality and often lifelong morbidity. Rh disease remains a significant global burden. Today the most common cause of neonatal AIHA in Western countries is ABO incompatibility, ie, infants with A or B antigen born to group O mothers with high-titer IgG antibodies. These infants may demonstrate isolated unconjugated hyperbilirubinemia rather than hyperbilirubinemia and anemia, which is more typical of Rh disease. Hyperbilirubinemia may be exacerbated by coexistent glucose-6-phosphate dehydrogenase (G6PD) deficiency or Gilbert syndrome. In addition to ABO incompatibility, prenatal alloimmunization to minor RBC antigens such as Kell, Fy, Jk, C, and E is also rising in relative frequency and may lead to severe disease.Onset of jaundice within the first postnatal day or prolonged or severe hyperbilirubinemia should prompt investigation of hemolytic disease. Infants with alloimmunization usually are DAT-positive. If the DAT result is negative, the laboratory performs an indirect antiglobulin test with the infant's serum. If agglutination occurs, maternal antibody is present in the serum. If the indirect antiglobulin test result is negative, a search for nonimmune or congenital causes of HA is warranted.Intensive phototherapy is often sufficient to address ABO-associated hemolytic disease, although exchange transfusion may be necessary. The use of intravenous immunoglobulin to prevent exchange transfusion is controversial, as demonstrated in a recent meta-analysis. (3) After discharge from the nursery, late-onset anemia may ensue 1 to 3 weeks after birth. Anemia results from continued immune-mediated destruction of RBCs and RBC progenitors as well as antibody-associated suppression of erythropoiesis. Neonates should be closely followed after discharge to determine the need for transfusion.Beyond the neonatal period, AIHA is rare in children, with an annual incidence of 0.2 per million individuals younger than age 20 years. A recent French national cohort study suggests the incidence may be as much as 10 to 20 times higher. (2) AIHA may be classified as primary or secondary.Primary AIHA, for which a cause is not identified, accounts for 30% to 40% of pediatric cases. Primary AIHA is further categorized by thermal reactivity or the temperature at which the RBC autoantibody is most reactive and causes agglutination. Agglutination at 37°C (98.6°F) constitutes warm AIHA, while agglutination below 30°C (86°F) is defined as cold AIHA (Table 2).Sixty percent of adult and pediatric patients with AIHA are diagnosed with warm agglutinins, which are almost always IgG but sometimes involve complement. Most of these patients were previously healthy but may have had nonspecific fever or viral symptoms. At diagnosis, patients present with jaundice, splenomegaly, and laboratory findings consistent with HA. If DAT is negative for anti-IgG but positive for anticomplement, further testing for cold agglutinins and paroxysmal cold hemoglobinuria (PCH) should be pursued.Cold agglutinin disease is caused by IgM autoantibodies, which bind below 37°C (98.6°F) and are maximally reactive at 4°C (39.2°F). IgM autoantibodies trigger complement deposition in vitro, resulting in agglutination with anticomplement. Patients may display acrocyanosis when cold, which results from autoagglutination of RBCs in the skin capillaries, causing localized stasis. Although bedside autoagglutination of the blood can be observed in the test tube as the sample cools, this may be a result of clinically insignificant cold autoantibodies. Further testing includes initial screening at room temperature (20°C [68°F]), which should induce agglutination in the presence of cold agglutinin disease. Subsequently, agglutination of the RBCs in saline and albumin is observed in a staged manner from 0° to 30°C (32° to 86°F). If agglutination occurs at 30°C (86°F), pathogenicity is inferred.PCH is a rare, self-limited AIHA caused by the Donath-Landsteiner (DL) antibody. Recurrence is unusual. Once commonly associated with syphilis, it is now seen predominantly in children, often preceded by an upper respiratory tract infection. The DL antibody is a cold-reactive IgG, which is considered biphasic because of the 2-step nature of its in vitro characteristics. The DL test involves incubation of the patient's blood at 4°C (39.2°F) for 1 hour to allow maximal binding of the IgG, followed by a second incubation at 37°C (98.6°F) to activate complement and induce hemolysis. The DL test is not universally available and may become negative after a few days into the clinical course of the condition, making diagnosis of PCH a challenging proposition. (4)DAT-negative AIHA may be present, particularly if cold antibodies are involved. Antibody may not be tightly bound to RBCs and may be eliminated with the eluate in vitro. DAT-negative AIHA may also involve IgA or natural killer (NK) cells, which are not routinely screened for by the standard DAT. (4) More detailed immunologic evaluation of the RBCs using flow cytometry, gel card diagnostics, or more sensitive Coombs reagents may be available through select reference laboratories.A triggering cause was identified in 63% of cases of AIHA in the French national cohort study, characterizing the condition as secondary. A defined infection was diagnosed in 22% of patients, and almost 50% of these individuals ultimately were diagnosed with an immune disorder. Associated organisms included Epstein-Barr virus, cytomegalovirus, Mycoplasma, pneumococcus, and parvovirus. (2)Although less common than in adults, pediatric autoimmune cytopenias can be associated with malignancies such as Hodgkin lymphoma. AIHA can be seen with autoimmune lymphoproliferative syndrome (ALPS), common variable immunodeficiency, systemic lupus erythematosus, and after solid organ and allogeneic stem cell transplantation. Disordered immune regulation through multifactorial mechanisms such as altered regulatory T-cell function, abnormal complement activity, and abnormal apoptosis predisposes these individuals to autoimmunity.An abrupt decline in hemoglobin values after initiation of certain medications should prompt consideration of drug-associated immune hemolytic anemia (DAIHA). The incidence of DAIHA is estimated at 1 per 1 million pediatric and adult patients, but this is likely an underestimate. Recognizing this potentially severe complication allows discontinuation of the drug and resolution of hemolysis. One proposed mechanism asserts that certain drugs bind covalently to RBC antigens, stimulating hapten-dependent antibodies that activate macrophages and Fc-mediated extravascular destruction. Another mechanism involves direct stimulation of RBC autoantibody production. Cefotetan, ceftriaxone, piperacillin, fludarabine, and diclofenac have been implicated. Specialized reference laboratories can perform drug-independent and -dependent assays to facilitate diagnosis.Corticosteroids (prednisone 1 mg/kg per day) are first-line therapy for warm AIHA and are associated with an 80% response rate. Improvement usually occurs within 24 to 72 hours of initiation. Once anemia is corrected, corticosteroids are weaned over several months to avoid relapse. Even after recovery, the DAT may remain positive for years or indefinitely. Recurrence is more likely if an underlying autoimmune disease or immunodeficiency exists. If the patient does not tolerate reduction of corticosteroids or if the agents are ineffective, second-line treatment is indicated. Both rituximab and splenectomy have been used but have not been compared in clinical trials.Splenectomy has been used as second-line therapy for refractory warm AIHA since the 1950s. There is no role for splenectomy in cold agglutinin disease because hemolysis in those cases is intravascular. There are surprisingly few data on the efficacy of splenectomy in children with refractory warm AIHA. Several large case series of adult patients undergoing splenectomy for benign hematologic diseases show that it is relatively safe, particularly if the spleen can be removed laparoscopically. Patients have an increased risk of thrombosis, especially affecting the portal or mesenteric veins, perhaps exacerbated by postsplenectomy thrombocytosis. However, the risk of thrombotic events may be more a function of the underlying hematologic disorder; thalassemia intermedia and major confer hypercoagulability. (5) The most feared complication is postsplenectomy sepsis due to encapsulated organisms. Splenectomy should be delayed in children younger than age 5 years because the risk of sepsis is greatest in this age group. Vaccination against encapsulated organisms, including the pneumococcal conjugate series and Haemophilus influenzae type b (Hib) series should be completed by 15 months of age. Pneumococcal polysaccharide and meningococcal polysaccharide can be administered after age 2 years and should be provided at least 2 weeks before splenectomy. Postsplenectomy, the patient should continue to receive antibiotic prophylaxis, usually penicillin, for at least 5 years or through age 18 years. The family must be educated about fever as an indicator of bacterial sepsis.Rituximab, a chimeric monoclonal antibody specific to the B-lymphocyte CD20 antigen, may supplant splenectomy as an alternative for corticosteroid-refractory AIHA. Rituximab efficiently eliminates B lymphocytes and has been used to treat other autoimmune diseases. The typical regimen is 375 mg/m2 weekly for 3 to 4 weeks. In a case series, 87% of patients had a sustained response at 13 months. Three of the 15 patients suffered recurrence but responded to a second course of rituximab. (6) The aggregate results of other small studies support a durable response to rituximab with few adverse effects. Infusion reactions include fever, hypotension, respiratory distress, and rash; these complications respond to infusion rate reduction and antihistamine use. Premedication with antipyretics, antihistamines, and corticosteroids usually prevents such reactions. Increased susceptibility to infection and viral reactivation are theoretical concerns but are infrequent and usually seen in patients undergoing stem cell transplant. (7) Rituximab has been used with success in some patients who have cytopenias associated with underlying immune disorders, (8)(9) although patients with AIHA associated with ALPS did not respond to rituximab. (10)Most cases of cold agglutinin disease result in chronic mild HA. Patients are advised to avoid the cold. Immunosuppressive therapy, such as corticosteroids, cyclophosphamide, chlorambucil, fludarabine, and rituximab, has been used without significant efficacy or durability of response. (11)Regardless of classification, if a patient ultimately diagnosed with AIHA presents with severe anemia that may cause cardiovascular compromise (hemoglobin <5 g/dL [50 g/L]) or severe anemia with reticulocytopenia, transfusion is necessary. Communication with the blood bank about the clinical scenario is imperative because autoantibodies often obscure the RBC phenotype and make crossmatching difficult. If the child has not been transfused before, it is reasonable to proceed with transfusion despite positive crossmatching tests because alloimmunization is rare. If the patient has received a previous transfusion, the blood bank performs specialized testing to clarify the presence of alloantibodies.Inherited molecular defects that affect the stability of the RBC, including its shape (SCD), hemoglobin content (thalassemia), membrane stability (spherocytosis), or metabolic stability (G6PD deficiency), can cause hemolysis. In this section, we review the pathophysiology, clinical presentation, and management recommendations for these congenital hemolytic anemias.SCD occurs in 1 in 300 to 400 African American births in the United States. The spectrum of SCD encompasses multiple sickling variants, which are diagnosed on newborn screen. The most common and most severe type is homozygous SS disease, in which both parents contribute the sickle hemoglobin mutation. The remaining genotypes are compound heterozygotes. Coinheritance of hemoglobins S and C as well as hemoglobin S and β-thalassemia occur to a lesser degree. In people of Asian descent, coinheritance of hemoglobins S and E is rising in incidence.Expression of sickle hemoglobin results from a point mutation in the β-globin gene. Deoxygenation causes abnormal polymerization of sickle hemoglobin, transforming the erythrocyte into the characteristic crescent or sickle shape. Vaso-occlusion by these poorly deformable RBCs is the hallmark of the disease, but there is extensive literature describing the molecular and cellular changes that contribute to SCD pathophysiology. (12)The spleen is also subject to multifactorial injury, invariably leading to splenic dysfunction early in life and ultimately autoinfarction. Before autoinfarction, the spleen can sometimes sequester blood cells. Splenic sequestration tends to occur in early childhood in those who have SS disease and later in patients with milder disease. Sequestration may vary from self-limited, with a mild drop in hemoglobin and splenomegaly, to severe, in which the volume of sequestered blood is life-threatening and patients present with cardiovascular collapse. Parents are taught to palpate their children's spleens because they may be the first to detect this may be considered for severe anemia. severe splenic sequestration may splenectomy in select cases. However, no data or in with in splenic function to infection with encapsulated organisms such as and Before in prophylaxis, children younger than age 3 years with SS disease pneumococcal with significant The of newborn prompt initiation of prophylaxis in and introduction of and pneumococcal have of sepsis and in infants with pneumococcal disease occurs, in those who have SCD must be Clinicians should at a a blood cell reticulocyte and blood and with in the of has for children who have of life is by and dysfunction. and chronic can lead to organ damage in patients with the most severe disease (Table The greatest has been in disease in of the natural study of SCD in the United that in of those who had SS disease by age 20 years. for most The risk of if SCD is from to but this risk is with chronic cause of in SCD is multifactorial and remains of the RBCs to the recurrent injury, a altered and in the of chronic anemia likely contribute to the of is a for the of of is on the that flow is to with flow flow on is of in those who have The in Anemia study that in patients with abnormal chronic transfusion to sickle hemoglobin to less than 30% was as primary of at age 2 is now a of for those who have severe SCD hemoglobin hemoglobin Once identified, patients are on RBC of transfusions, after findings was associated with to abnormal as well as increased rate of in the 2 The standard of is to continue chronic with are as a risk for in those who have with age and is estimated to be to by age are more common those who have SS disease but are also in other sickle variants. as on without have been associated with and as well as a risk for should be of these that may receive a recent results from the that chronic of However, it is this affect the of the study and the of for screening in this are the most common of the global population a mutation related to or The a spectrum of of or production due to of point and less In addition to the resulting excess of that on RBC membrane and E is a β-globin common in Asian the a it be can be by with hemoglobin In healthy 2 on are The 4 2 which with 2 to fetal hemoglobin in and for several months after birth. production a from to months of which to of β-globin rather than The β-globin with the 2 to adult demonstrate a between and of 1 is carrier because it is clinically minor or individuals may exhibit mild anemia that does not or with and sickle cell anemia can the of disease, or can be diagnosed at or later in At to production as well as of which is identified as hemoglobin on newborn screen. After the of β-globin are identified as hemoglobin on hemoglobin The by hemoglobin results in chronic hemolysis. Patients may RBC during their second of need for transfusions, patients with hemoglobin disease are at risk for due to increased has been incompatible with life due to the to fetal and in leading to and a However, intrauterine have some patients to the period, with the sequelae of congenital and chronic after and marrow contrast to β-globin is by a on More than point can cause with variable of 1 mutation to β-thalassemia or a benign condition characterized by mild anemia. Clinicians may β-thalassemia when a child who has mild anemia to hemoglobin on hemoglobin electrophoresis and results of studies the intermedia results from of 2 β-globin 1 of which a mild patients are not but may be at risk for and from chronic transfusion may be Patients with thalassemia intermedia may also due to and they from of 2 severe β-globin in a homozygous or compound causes β-thalassemia and to in the second months after as fetal hemoglobin and anemia If the disease remains the stigmata of including as the marrow to hepatosplenomegaly and due to and due to chronic anemia in an who has and should prompt investigation for β-thalassemia electrophoresis in diagnosis. The child should be to pediatric for initiation of chronic transfusions, which erythropoiesis. and Patients are transfused every 2 to 4 weeks to a hemoglobin of to 10 g/dL of blood to of most of which be The excess the capacity of the is is in organ causing patients are at risk for and other standard of is via Most use as a marker for with of the and as an method of Most children are on or at age 2 years. These agents bind and facilitate its and a donor is some children with β-thalassemia may be for stem cell