Dr. Connie Westhoff from the New York Blood Center joins Dr. Chaffin to discuss Rh genotyping in pregnant ladies and potential transfusion recipients with unexpected results on serologic D typing. Most laboratorians are aware that testing a patient for the D antigen can be challenging, especially when the results differ from previous results or if the reactions are “weaker than expected.” Dr. Westhoff helps us navigate this challenging area with an awesome summary of the basics of RhD testing, why and how the results can vary, a description of weak D and partial D, and finally, a potential management strategy for donors with unexpected results. If D testing has confused you, or if you don’t “get” weak or partial D, this is the episode for you!