REFERENCES 339 8 De Buys Roessingh AS, Lagausie P, Rohrlich P, Berrebi D, Aigrain Y. 2002. Follow up of partial splenectomy in children with hereditary spherocytoisis. J Pediatr Surg 37:1459–1463. 9 Sandoval C, Srtringel G, Weisberger J, Jayabose S. 1997. Failure of partial splenectomy to ameliorate the anemia of pyruvate kinase deficiency. J Pediatr Surg 32:641–642. This page intentionally left blank SECTION VIII Immune Dysfunction Copyright © 2008 by The McGraw-Hill Companies, Inc. Click here for terms of use. This page intentionally left blank CHAPTER 18 ERYTHROBLASTOSIS FETALIS (IMMUNE HEMOLYTIC DISEASE OF THE NEWBORN) ETIOLOGY OF IHDN 343 THE Rh ANTIGEN CULPRIT IN IHDN 344 Rh SENSITIZATION 345 CLINICAL ASPECTS OF IHDN 346 ABO HEMOLYTIC DISEASE OF THE NEWBORN 348 In 1932, Dr. Louis K. Diamond and associates suggested that a single pathological process produced three supposedly distinct hematological syndromes of the newborn infant: universal edema (hydrops fetalis); anemia of the newborn; and icterus gravis neonatorum. 1 The new designation, erythroblastosis fetalis, emphasized the abundant presence of nucleated red cells in the blood and extramedullary organs of affected fetuses and infants. The decades following this description saw the discovery of the cause of erythroblastosis fetalis and the introduction of a series of diagnostic and therapeutic interventions that reduced the morbidity and mortality associated with the condition. Most importantly, the introduction of preventive measures has virtually eradicated the condition in much of the world. The story of the identification, treatment, and prevention of erythroblastosis fetalis, or immune hemolytic disease of the newborn (IHDN), is one of the great medical triumphs of the twentieth century. ETIOLOGY OF IHDN IHDN is a subset of the disorders discussed in the chapter on immune-mediated hemolysis (Chapter 19), which include autoimmune hemolytic anemia and 343 Copyright © 2008 by The McGraw-Hill Companies, Inc. Click here for terms of use. 344 IMMUNE DYSFUNCTION SECTION VIII transfusion-induced hemolysis. The former condition is a frankly pathologic state most commonly involving an immune regulatory system gone amok. The latter is an iatrogenic problem related to the introduction of foreign material (transfused red cells) into the blood stream. IHDN is a blend of the two whose origin lies in the special relationship that exists between the mother and fetus. A partial state of immune tolerance allows the temporary coexistence of two genetically and antigenically distinct individuals. The tolerance is precarious with its integrity depending on the powerful physical barrier created by the placenta. The placenta is the gatekeeper that employs specific transport mechanisms to supply building blocks to the fetus while removing potentially toxic substances from the fetal environment. The maternal and fetal circulations come into close juxtaposition in the placenta but do not commingle. The placenta has specific transport machinery to supply ma- ternal antibodies of the IgG class to the fetus. These provide important protection to the immunologically immature newborn against pathogens that after birth descend like flies. The happy state functions flawlessly millions of times each year. However, on occasion problems do arise. THE Rh ANTIGEN CULPRIT IN IHDN The Rh antigen (Rhesus, referring to the important role this primate played in the early antigen characterization) is one of the many glycoprotein families expressed on the red cell membrane. Glycoproteins are quite immunogenic and most provoke some degree of antibody production when introduced into a foreign environment. Most of the red cell membrane glycoproteins have no assigned function, although they all presumably have some physiological role. The Rh proteins are part of an ancient and ubiquitous gene superfamily whose original members had a role in the regulation of cellular ammonium transport. 2 The current Rh gene family seen on red cells diverged from the primordial gene millions of years ago. Although the Rh proteins might have a residual role in ammonium homeostasis, the point remains open. 3 The Rh blood group is widely expressed on red cells. The family has many members that differ by small structural variations. In the context of IHDN, the Rh D group is the key component. In routine clinical usage, the term “Rh positive” refers to red cells that express the Rh D antigen, ignoring all other Rh antigens. Red cells that lack Rh D are designated as “Rh negative.” The importance of the Rh D antigen lies in what appears to be a historical genetic anomaly. Most likely, in the anthropologically distant past all human red cells expressed the Rh D antigen. At some point in Europe, a mutation caused the loss of RHD gene expression. 4 Over time, the proportion of the Rh D-negative gene rose in the population to the point that currently about 15% of Caucasians are Rh D-negative. This remarkably high figure must reflect some past selective advantage since this is the sole means by which a variant can attain such a high gene frequency. The Rh D-negative phenotype is much less common in other ethnic groups. The 7–8% incidence of the Rh D-negative phenotype seen in African Americans likely reflects CHAPTER 18 ERYTHROBLASTOSIS FETALIS 345 genetic admixture with Europeans. The Rh D-negative phenotype is fleetingly rare in East Asian peoples. 5,6 Rh SENSITIZATION Rh sensitization requires a specific clinical scenario in which the mother is Rh D- negative and the fetus is Rh D-positive. 7 The gene for Rh D expression in the fetus comes from the father, of course. However, several other factors must convene to trigger the production of antibodies to Rh D by the mother. Most obviously, fetal blood must break the placental barrier and enter the ma- ternal circulation. The likelihood of an antibody response rises with the volume of the leak. During the course of pregnancy, fetal red cells intermittently gain access to the maternal circulation in quantities ranging from 0.1 to 1.0 mL. These repeated small trespasses appear to provoke the antibodies against the Rh D antigen in the Rh D-negative mother. 8 Greater immunization occurs with the larger transplacental hem- orrhages that accompany processes that severely disrupt the integrity of the placental barrier, such as toxemia. The largest risk of fetal to maternal blood transfer occurs at delivery. Rare causes of Rh D antigen sensitization include midtrimester spontaneous abortion and blood transfusion. The Kleihauher-Betke stain allows simple detection of fetal red cells in the mater- nal circulation. 9 The test takes advantage of the relative resistance of fetal hemoglobin to alkaline denaturation. Maternal cells appear as washed-out ghosts while fetal cells stand out following the staining. Imprecise and subjective readouts often counter- balance the simplicity of this test. Fluorescence-activated cell sorter analysis using antibodies specific to human fetal hemoglobin or to Rh D detects minute numbers of fetal cells in the maternal circulation. Florescence microscopy is an alternate way to use this newer technology. 10 Without preventive intervention, about 15% of Rh D-negative mothers will de- velop antibodies to Rh D during their first pregnancy where the fetus is Rh D-positive. Successive such pregnancies increase both the incidence of antibody production and its titer. For this reason, the severity of erythroblastosis fetalis increases with succes- sive pregnancies in women so unfortunate as to suffer repetitions of the problem. Other factors influence the rate and risk of Rh D immunization. Fetal red cells with a high density of Rh D antigen on the membrane are more likely to provoke an antibody response than are cells with a low antigen density. 11 Phenotypic char- acteristics of the father influence red cell density Rh D antigen. Interestingly, ABO incompatibility between mother and fetus lowers the risk of Rh immunization. The key fact in this setting is that the antibodies directed against ABO blood group anti- gens primarily are of the IgM class. IgM antibodies do not cross the placental barrier, thereby minimizing any hemolysis in utero. Furthermore, IgM antibodies directly and quickly lyse fetal red cells that cross into the maternal circulation. Few fetal cells reach the macrophage/lymphocyte system to prompt production of IgG antibodies against the Rh D antigen. 346 IMMUNE DYSFUNCTION SECTION VIII CLINICAL ASPECTS OF IHDN The disease has a wide spectrum of severity that correlates with the level of maternal antibodies. First pregnancies are rarely affected. All pregnant women should have red cell grouping and typing in early pregnancy. Rh D-negative women should have their serum examined for the presence of anti-D antibodies by midtrimester. Should the mother have anti-D antibody, antibody titer determinations are in order. When the anti-D titer is high, the degree of fetal involvement is assessed. In the most severely afflicted fetuses, the hemolytic process is so extreme that a progressively more severe anemia occurs in the midtrimester. In some fetuses, the anemia is extreme to the point of provoking congestive heart failure, resulting in universal edema and often in fetal death. At times, neutropenia and thrombocytopenia occur in association with the extreme anemia. Infants at high risk for intrauterine death can be salvaged by intrauterine transfusions and exchange transfusions permitting them to remain in utero until they attain a level of maturity consistent with safe delivery. 12 Somewhat less severely affected infants are born alive, although they usually have substantial anemia with associated marked hepatosplenomegaly due to ex- tramedullary hematopoiesis. Hyperbilirubinemia at the time of delivery is typical. The hemoglobin value at birth usually is less than 13.0 g/dL. The direct antiglobulin (Coombs’) test is positive, reflecting antibody directed against the Rh D antigen. A plethora of nucleated red cells exist on the peripheral smear, true to the term ery- throblastosis fetalis (Figure 18-1). The high level of unconjugated bilirubin at birth FIGURE 18–1 Blood smear from a neonate with erythroblastosis fetalis. Erythroblasts of nearly all stages of normal development are present, accompanied by numerous polychro- matophilic cells, scattered poikilocytes, and small numbers of spherocytes. (From Jandl JH. 1987. Blood: Textbook of Hematology. Boston: Little, Brown and Company. Figure 9-2, p. 293. With permission from the publisher.) CHAPTER 18 ERYTHROBLASTOSIS FETALIS 347 rises following delivery since the placental connection is severed and the option of shunting the metabolite to the maternal circulation for disposal is lost. Severe hyperbilirubinemia is the primary basis of morbidity and mortality in infants born with erythroblastosis fetalis. The high bilirubin level in these infants reflects both red cell destruction and the limited capacity of the liver to metabolize the compound. 13 Hyperbilirubinemia can cause severe neurological disease (kernicterus) and even death. Frequent sequelae of kernicterus include mental retardation, cerebral palsy, and deafness. The immature blood–brain barrier of the newborn cannot prevent free bilirubin in the plasma from entering the brain and damaging neurons. Albumin has a carrying capacity for bilirubin that approximates 20 mg/dL. Beyond this level the toxic metabolite is free in the plasma and able to cross into the neonate’s brain. Successful efforts that control bilirubin and maintain values below 20 mg/dL pre- vent most cases of kernicterus and its severe neurological consequences. Exchange transfusion through the umbilical vein is an effective means to this end. 14 The proce- dure involves the intermittent aspiration of 10–20 mL of fetal blood from the umbilical vein and its replacement with whole blood that is Rh negative and compatible with the mother’s serum. An exchange volume of approximately twice the blood volume replaces 90% of the infant’s red cells. A concentrated albumin solution is some- times infused prior to the exchange absorbs additional bilirubin that is subsequently removed with the exchange procedure. Bilirubin levels of mildly affected babies with less extreme hemolytic anemia can be near normal at birth but increase by 1–2 mg/dL daily to dangerously high postnatal levels. Such neonates usually require exchange transfusions but often they can be controlledbyphototherapy.These infants are however at risk of developing very severe anemia in the first month of life because of the short survival of antibody-coated red cells. Close monitoring of these infants for the first 6–8 weeks of life is essential. Some require a simple transfusion with Rh D-negative red cells to stave off problems. In the 1960s, prevention of Rh D isoimmunization and clinical erythroblasto- sis became possible. 15,16 Two groups, one in New York and the other in England, demonstrated that intravenous administration of anti-Rh immunoglobulin (Rhogam) to nonimmunized Rh D-negative mothers immediately postpartum could prevent pri- mary immunization. The precise mechanism is not fully established, but a major reason could be that the antibody destroys fetal Rh D-positive red cells that have entered the maternal circulation in the peripartum period before they can evoke an immunological response in the mother. This procedure has produced dramatic results. The incidence of erythroblastosis fetalis due to Rh D sensitization has decreased so greatly that it now is a rare disease in the United States and Europe. The gratifying outcome is that many physicians trained in recent decades have never seen the disorder. Far less commonly, erythroblastosis fetalis results from maternal sensitization to other red cell antigens of the Rh system including C, c, and e. Antigens outside the Rh family such as Kell, Duffy, Kidd, and S/s on occasion produce similar problems if the mother lacks these antigens while carrying a fetus who expresses them. In the event of exchange transfusion to control hyperbilirubinemia, the transfused RBC should lack the offending blood group. 348 IMMUNE DYSFUNCTION SECTION VIII ABO HEMOLYTIC DISEASE OF THE NEWBORN About 60% of persons lack A or B antigens on their RBC and are designated as having blood group O. Group O individuals have naturally occurring anti-A and anti- B antibodies in their serum (hemagglutinins). These antibodies are usually of the IgM class and so do not cross the placenta. However, some pregnant women occasionally develop IgG anti-A or anti-B antibodies that cross the placenta and induce hemolysis of either A-positive or B-positive fetal red cells. Most commonly, ABO hemolytic disease of the newborn involves an infant with blood group A and a mother with blood group O. ABO erythroblastosis does not cause severe anemia in the fetus, so hydrops fetalis does not occur. Reticulocytosis exists at birth but the affected newborn usually lacks significant anemia. The blood smear shows polychromasia, a few nucleated RBCs, and intense spherocytosis. The direct Coombs’ test (DAT) is usually positive, but can be weakly so. Jaundice often occurs in the first 24 hours of life, and monitoring of the serum bilirubin level is important. Extreme hyperbilirubinemia can require exchange transfusion or phototherapy to prevent kernicterus and its complications. In interesting contrast to IHDN due to Rh D incompatibility, hemolysis in the newborn due to ABO incompatibility occurs significantly more frequently in African American TABLE 18-1 KEY DIAGNOSTIC POINTS IN IHDN Issue Manifestaion Approach Maternal immunization to Rh D • Rising antibody titers to Rh D • Monitor antibody titers during pregnancy. • RhoGam immunization at delivery. Hemolysis of fetal red cells • Fetal hemolytic anemia • Intrauterine transfusion or exchange transfusion through an umbilical or placental vein for severe anemia, to permit the extension of gestation. Postpartum hyperbilirubinemia • Rising neonatal bilirubin levels (20 mg/dL is extremely severe) • Exchange transfusion and/or phototherapy. Anemia in early infancy Declining infant hemoglobin level • Simple transfusion with Rh D-negative red cells. [...]... for, 103 107 peripheral blood smear, 102 103 Plummer-Vinson abnormality in adults, 102 Blue sclerae due to, 102 as cause of anemia, 33 causes of, 108 t, 109 – 110 dysfunctional uterine bleeding, 112 enteric mucosa disruption, 110 111 functional bowel loss, 111 gastrointestinal blood loss, 112–113 iron absorption inhibition, 109 – 110 physiological blood loss, 111–112 poor bioavailability, 108 109 structural... hemolysis or red cell sensitization .10 The drug induces red cell autoantibodies in 10 20% of patients after 4 or more months of use These red cell antibodies are true autoantibodies directed against red blood cell membrane antigens rather than the drug or a drug-altered antigen The target membrane antigen is usually within the Rh system, although often the antibody specificity is elusive A warm-reacting... children, 99 long-term effects of, 100 peripheral blood smear of, 103 f treatments of oral iron supplementation, 116–119 parenteral iron supplementation, 119–121 iron-deficient erythrocytes, 14 iron dysregulation states, 121 iron overload and PK deficiency, 322 in pregnancy, 53–54 iron status assessment tests serum ferritin level, 105 107 serum iron, 105 107 total iron-binding capacity (TIBC), 105 107 iron supplementation,... 208 and pediatric myelodysplasia, 220–221 platelet disturbances in, 210 pseudo-Pelger-Huet anomaly, diagnostic feature, 209 INDEX RAEB-1 and RAEB-2 subcategories, 218 supportive therapy for, 229–231 symptoms of, 209 and therapy/treatment-related myelodysplasia, 219t, 220 myelogenous leukemia, 211, 323 myeloid metaplasia, 21 myeloid-to-erythroid ratio (M:E ratio), 139 myelophthesis, 16, 60 N NADPH-dependent... Circulation Packed Red Cells Antibody 4 Antibody 3 Endogenous Red Cells Normoblast Transfused Red Cells Antibody 2 Antibody 1 Lymph Node Schematic representation of the components of immune-mediated hemolysis Blood in the circulation is primarily produced in and released from the bone marrow as shown in the lower left of the figure Transfusion shown in the upper right is the other way that red cells enter... defects, 111 during childhood, 99 100 impacts on neonates and childs, 49, 123t with coexisting inflammation, 123 impacts on MCH and MCHC, 103 effects on erythrocyte production, 103 , 113–114 koilonychia, disbalanced keratin formation, 102 in menstruating females, 123t Pica due to, 102 during pregnancy and its assesment, 50–53 and thrombocytosis, 103 siderophores, iron-binding molecules, 98 states of,... of iron and erythropoietin, 115f metabolism and G6PD deficiency, 314–317 production, iron as key component, 62–63 protection mechanism to malaria, 86–90 red cell aplasia associated with Parvovirus B19 infection, 188–189 red cell distribution width (RDW) value, 11 red cell fragmentation syndrome, 59 red cell membrane cytoskeleton, 332, 332f refractory anemia, 211 cytopenia, peripheral blood cell line... malaria, 87–88sideroblastic anemias, 46, 221 acquired sideroblastic anemias vs hereditary, 223 categories of, 223 disturbed heme metabolism and, 223 drug- and toxin-induced, 228–229 inhibits heme biosynthetic pathway, 228 enzymes relevant to (ALAS-2 or ALAS-e), 224 feature of, mitochondrial iron deposition, 224 374 refractory anemia with ringed sideroblasts, 213 siderophores, iron-binding molecules, 98... of genes and proteins in erythroid cells and nonerythroid tissues Blood Cells Mol Dis 27:90 101 Colin Y, Cherif-Zahar B, Le Yan Kim C, Raynal V, Yan Huffel V, Cartron JP 1991 Genetic basis of the RhD-positive and RhD-negative blood group polymorphism as determined by Southern analysis Blood 78:2747–2752 Salmon D, Godelier M, Halle L, et al 1988 Blood groups in Papua New Guinea Eastern Highlands Gene... limited production of red cells by an erythron that generates all other blood components without difficulty The severe and selective anemia is part of a process called pure red cell aplasia that falls best under the rubric of aplastic anemia COOMBS’ TEST OR DIRECT ANTIGLOBULIN TEST The Coombs’ test or direct antiglobulin test (DAT) is so vital to the understanding and evaluation of immune-mediated hemolysis . Maternal cells appear as washed-out ghosts while fetal cells stand out following the staining. Imprecise and subjective readouts often counter- balance the simplicity of this test. Fluorescence-activated. have red cell grouping and typing in early pregnancy. Rh D-negative women should have their serum examined for the presence of anti-D antibodies by midtrimester. Should the mother have anti-D antibody,. polychro- matophilic cells, scattered poikilocytes, and small numbers of spherocytes. (From Jandl JH. 1987. Blood: Textbook of Hematology. Boston: Little, Brown and Company. Figure 9-2 , p. 293. With