A 40 year old woman requires a hysterectomy and her doctor orders a type and screen. She initially tests as group O, Rh negative and has a negative antibody screen. The blood bank is experiencing a summertime shortage of blood, so the patient is also tested for the weak D phenotype. Her weak D test shows 2+ agglutination. However, a direct antiglobulin test shows 2+ agglutination using anti-IgG and 3+ using anti-C3.

What is the weak D phenotype of this patient?
Should the patient receive Rh-positive or Rh-negative cell units for transfusion?

The patient experienced unexpected bleeding during surgery and received 2 Rh-negative units. Six months later she was in an automobile accident and was tested for unexpected antibodies and anti-D was identified. A serologic work up excluded the presence of anti-G and anti-C. The patient is not an IV drug user and received no other transfusions since her hysterectomy.

Is it possible that this patient developed anti-D as a result of the transfusion episode six months ago? if so, how?
What is the risk of sensitization if an Rh-negative patient receives Rh-positive or weak D positive and what is the risk of serious complications?