What is the role of a CBC count in the workup of hemolytic disease of the newborn (HDN)?

Updated: Dec 28, 2017
  • Author: Sameer Wagle, MBBS, MD; Chief Editor: Muhammad Aslam, MD  more...
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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:

  • Anemia: Measurements are more accurate using central venous or arterial samples rather than capillary blood.

  • 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).

  • 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.

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