If a baby's cord hemoglobin is normal but the direct antiglobulin test is positive, does the baby have hemolytic disease of the newborn (HDN)?

In this scenario, a positive direct antiglobulin test (DAT) indicates the presence of maternal antibodies coated on the baby's red blood cells, which can lead to hemolytic disease of the newborn (HDN). The condition is characterized by the destruction of red blood cells in the baby, usually due to incompatibilities in blood type, commonly between Rh or ABO factors.

Although the cord hemoglobin is reported as normal, this does not rule out the possibility of HDN. The reason for this is that the hemoglobin levels in the newborn can still be within a normal range initially, even if hemolysis has begun, as the body may be compensating at that point. The positive DAT alone is a strong indication of hemolysis being present, suggesting that maternal antibodies are interacting with the baby's red blood cells. Therefore, the presence of these antibodies is a key factor in diagnosing HDN, which is supported by the positive DAT.

Other factors, such as cord bilirubin levels, are also important in the overall clinical assessment, but the positive DAT alone substantiates a diagnosis of HDN regardless of the initial cord hemoglobin reading. Thus, the indicated choice correctly recognizes that the positive DAT indicates the possibility of HDN despite the normal hemoglobin