Why might a patient with a weak D phenotype be at risk of forming anti-D antibodies when tested on the Ortho Provue system?

The correct selection highlights a critical issue in interpreting the Rh typing for patients with a weak D phenotype. When a patient presents with a weak D phenotype, there may be low levels of D antigen on their red blood cells. Depending on the testing system used—like the Ortho Provue—the results could misclassify the individual as Rh negative. This misclassification occurs because the weak expression of the D antigen might not be strong enough for the system to detect it as positive.

If the patient is incorrectly typed as Rh negative, they may then receive Rh-negative blood in transfusions. However, individuals with a weak D phenotype still have some level of D antigen, and transfusing them with Rh-negative blood could lead to the formation of anti-D antibodies over time, especially if their immune system encounters Rh-positive red blood cells in future transfusions or pregnancies. This patient could respond immunologically against the Rh-positive red blood cells if exposed, resulting in anti-D antibody formation.

This underscores the importance of accurately typing patients with weak D to prevent potential adverse outcomes, including the development of alloantibodies that can complicate future transfusions and pregnancies.