HEMOLYTIC DISEASE LAB STUDIES

hemolytic disease lab studies :
• CBC: The severity of hematologic abnormalities is directly proportional to the severity of hemolysis and extent of hematopoiesis. The following abnormalities are observed:
o Anemia: Measurements are more accurate using central venous or arterial samples rather than capillary blood.
o Increased nucleated 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. A low reticulocyte count is observed in fetuses provided with intravascular transfusion in utero and with Kell alloimmunization.
o 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).
o 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.

• Metabolic abnormality: Hypoglycemia is common and is due to islet cell hyperplasia and hyperinsulinism. 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 tests
o Indirect Coombs test and direct antibody test (DAT) results are positive in the mother and affected newborn. The maternal titers are the highest dilution of maternal serum at which a positive agglutination test result is obtained. Unlike Rh alloimmunization, DAT results are positive in only 20-40% of infants with ABO incompatibility. This is because fetal RBCs have less surface expression of type-specific antigen compared to adult cells.
o Although the indirect antiglobulin test result (neonate's serum with adult A or B RBCs) more commonly is positive in neonates with ABO incompatibility, it 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.
o 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 DAT result. On the other hand, significant hemolysis is associated with a negative DAT result when IgG1 and IgG3 are predominant antibodies, which are in low concentration but have strong lytic activity, crossing to neonatal circulation.

Imaging Studies:
• Perinatal ultrasonography: High-resolution ultrasonography has been a major advance in detection of early hydrops, and it 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.