Laboratory Studies
The diagnosis and management of pregnant women with hemolytic disease of the newborn (HDFN) is based on laboratory and radiographic monitoring. [13]
Hemolytic disease of the newborn is characterized by one or more of the following clinical presentations [33] :
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Rapidly progressive severe hyperbilirubinemia or prolonged hyperbilirubinemia
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Positive maternal antenatal antibody findings and/or diagnosis of anemia or fetal hydrops
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Positive neonatal direct Coombs test (direct antiglobulin test)
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Hemolysis on blood film findings
The severity of hematologic abnormalities is directly proportional to the severity of hemolysis and the extent of hematopoiesis. The following abnormalities are observed on complete blood cell (CBC) count findings:
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Anemia: Measurements are more accurate using central venous or arterial samples rather than capillary blood.
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Increased nucleated red blood cells (RBCs), reticulocytosis, polychromasia, anisocytosis, spherocytes, and cell fragmentation
The reticulocyte count can be as high as 40% in patients without intrauterine intervention.
The nucleated RBC count is elevated and falsely elevates the leukocyte count, reflecting a state of erythropoiesis.
Spherocytes (< 40%) are more commonly observed in cases of ABO incompatibility. Glucose does not correct the autohemolysis in ABO incompatibility unlike hereditary spherocytosis.
In severe hemolytic disease, schistocytes and burr cells may be observed, reflecting ongoing disseminated intravascular coagulation (DIC).
In neonates with sepsis, risk factors for DIC include asphyxia, bleeding, and gram-negative bacterial infection. [34]
A low reticulocyte count is observed in fetuses provided with intravascular transfusion in utero and with Kell alloimmunization.
Abnormally elevated mean cell hemoglobin concentration (MCHC) and red cell distribution width (RDW) values should prompt a diagnosis of hereditary spherocytosis. [35]
-
Neutropenia: This condition seems to be secondary to stimulation of erythropoiesis in favor of myelopoiesis. However, neutrophilia can be observed after intrauterine transfusion because of an increase in circulating cytokines (granulocyte-macrophage colony-stimulating factor).
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Thrombocytopenia: This condition is common, especially after intrauterine or exchange transfusions because of platelet-poor blood product and suppression of platelet production in favor of erythropoiesis.
Hypoglycemia is common and is due to islet cell hyperplasia and hyperinsulinism. [36] The abnormality is thought to be secondary to release of metabolic byproducts such as glutathione from lysed RBCs. Hypokalemia, hyperkalemia, and hypocalcemia are commonly observed during and after exchange transfusion.
Serologic test findings include the following:
-
Indirect Coombs test and direct antibody test results are positive in the mother and affected newborn. Unlike Rh alloimmunization, direct antibody test results are positive in only 20-40% of infants with ABO incompatibility. [37] In a recent study, [38] positive direct antibody test findings have a positive predictive value of only 23% and a sensitivity of only 86% in predicting significant hemolysis and need for phototherapy, unless the findings are strongly positive (4+). This is because fetal RBCs have less surface expression of type-specific antigen compared with adult cells. A prospective study has shown that the titers of maternal immunoglobulin G (IgG) anti-A or anti-B may be more helpful in predicting severe hemolysis and hyperbilirubinemia. The sensitivity and specificity of IgG titers of 512 or higher in predicting need for invasive intervention was 90% and 73%, respectively. [39] In a retrospective study (2005-2014) in a regional Belgian population, routine testing of maternal serum for relevant erythrocyte antibodies showed that in mother with positive antibodies, significant hyperbilirubinemia was noted more often if cord direct antiglobulin test (DAT) was positive (15% vs 2.6%). [40] Significant hyperbilirubinemia was was noted in 7%, 11%, and 27%, respectively, in those with clinically relevant erythrocyte antibodies, anti-A and anti-B.
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Although the indirect Coombs test result (neonate's serum with adult A or B RBCs) is more commonly positive in neonates with ABO incompatibility, it also has poor predictive value for hemolysis. This is because of the differences in binding of IgG subtypes to the Fc receptor of phagocytic cells and, in turn, in their ability to cause hemolysis.
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IgG2 is more commonly found in maternal serum but has weak lytic activity, which leads to the observation of little or no hemolysis with a positive direct antibody test result. On the other hand, significant hemolysis is associated with a negative direct antibody test result when IgG1 and IgG3 are predominant antibodies, which are in low concentration but have strong lytic activity, crossing to neonatal circulation.
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In newborns with hemolytic disease due to anti-c or anti-C antibodies, direct antibody test results may be negative, and the diagnosis is established after indirect Coombs testing.
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More recent studies on antibody characteristics have shown that lower core fucosylation of Rh-D antibodies while glycosylation and sialylation of anti-c antibodies significantly correlated with disease severity and fetal/neonatal disease. [41]
Obtain paternal molecular RhD zygosity testing. In addition, fetal RhD genotyping via cell free fetal DNA testing has become increasingly accurate in detecting fetal RhD allosensitization. [3]
Table. Comparison of Rh and ABO Incompatibility (Open Table in a new window)
Characteristics |
Rh |
ABO |
|
Clinical aspects |
First born |
5% |
50% |
Later pregnancies |
More severe |
No increased severity |
|
Stillborn/hydrops |
Frequent |
Rare |
|
Severe anemia |
Frequent |
Rare |
|
Jaundice |
Moderate to severe, frequent |
Mild |
|
Late anemia |
Frequent |
Rare |
|
Laboratory findings |
Direct antibody test |
Positive |
Weakly positive |
Indirect Coombs test |
Positive |
Usually positive |
|
Spherocytosis |
Rare |
Frequent |
|
Carboxyhemoglobin (COHb) values measured with a CO-oximeter appear to have the potential to confirm hemolysis in infants with ABO alloimmunization. [42] In a prospective study of 86 term jaundiced newborn infants, with or without hemolysis, and healthy controls, infants with ABO hemolytic disease had higher COHb values compared to the healthy control infants and newborns with hyperbilirubinemia without hemolytic disease, but no significantly higher value in COHb results was found between the hyperbilirubinemia without hemolytic disease group and the healthy control group. A cut-off value of 1.7% COHb was 72% sensitive and 97% specific for confirming hemolysis in ABO alloimmunization. [42]
Imaging Studies
High-resolution ultrasonography has been a major advance in detection of early hydrops and has also reduced the fetal trauma and morbidity rate to less than 2% during percutaneous umbilical blood sampling (PUBS) and placental trauma during amniocentesis. High-resolution ultrasonography has been extremely helpful in directing the needle with intraperitoneal transfusion (IPT) and intravascular transfusion (IVT) in fetal location.
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Liley curve. This graph illustrates an example of amniotic fluid spectrophotometric reading of 0.206, which when plotted at 35 weeks' gestation falls into zone 3, indicating severe hemolytic disease.
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Modified Liley curve for gestation of less than 24 weeks showing that bilirubin levels in amniotic fluid peak at 23-24 weeks' gestation.
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Queenan Curve: Modified Liley curve that shows delta-OD 450 values at 14-40 weeks' gestation.
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Slopes for peak systolic velocity in middle cerebral artery (MCA) for normal fetuses (dotted line), mildly anemic fetuses (thin line), and severely anemia fetuses (thick line).
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Management of first affected pregnancy.
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Management of pregnant women with previously affected fetus.
Tables
Characteristics |
Rh |
ABO |
|
Clinical aspects |
First born |
5% |
50% |
Later pregnancies |
More severe |
No increased severity |
|
Stillborn/hydrops |
Frequent |
Rare |
|
Severe anemia |
Frequent |
Rare |
|
Jaundice |
Moderate to severe, frequent |
Mild |
|
Late anemia |
Frequent |
Rare |
|
Laboratory findings |
Direct antibody test |
Positive |
Weakly positive |
Indirect Coombs test |
Positive |
Usually positive |
|
Spherocytosis |
Rare |
Frequent |
|
