Serological comparison of weak D versus weakly reacting D by four different methods

Weak D red cells were defined as having a reduced amount of D antigen (formerly called "Du") that required an indirect antiglobulin test (IAT) for detection. Weakly reacting D is those which give <2+ reactions on routine methods. The present study is sharing our experience on weak D and weakly positive anti-D in various methods.

All the blood sample of patients and blood donor, which were RhD negative, were included in the study. Furthermore, RhD positive sample <2+ was included. We repeated blood grouping of all these samples by gel card (Tulip), tube method (two different antisera), slide method, and Solid Phase Red Cell Adherence (SPRCA) (Immucore, USA).

A total number of samples were 27,245. RhD negative found out to be 945 (3.46%). Out of all, 929 (98.3%) samples were Rh D negative in gel card and IAT negative, while 16 (1.7%) were weak D positive. Rh D typing with these samples by different antisera at four platforms showed that 14 were weakly positive (<2+) in any of the four platforms. Similarly, out of 26,300 Rh D Positive samples, 21 samples (0.079%) were serologically weak (<2+). Repeat Rh D typing was done with different antisera in all four platforms. Result showed more than 50% were Rh D negative in any of four platforms.

Above observation showed that serological tests at various platforms failed to distinguish weak D from weakly reacting D. Thus, we propose that weakly reacting D should be treated equal as weak D unless they are distinguished by genotyping.