On the complexity of D antigen typing: a handy decision tree in the age of molecular blood group diagnostics.

RH is the most complex of all 29 blood group systems. New discoveries relating to the RHD gene, and an appreciation of its variant phenotypes such as weak D and partial D, have challenged the way that D status is assigned to both blood donors and blood product recipients. This concise review introduces the current concepts of weak D and partial D and how the identification of these variants has influenced the testing methods for the D antigen. We demonstrate how molecular tests of the RHD gene can and should be used in resolving serological discrepancies, in particular in pregnant women.