RhD Grouping

• RhD grouping has become more complex over the years as more monoclonal D reagents become available.
• For recipient testing, a single IgM monoclonal D reagent should be used. This reagent should be insensitive to D^VI
  • D^VI is the D variant most commonly associated with anti-D production.
  • There is minimal evidence that foetal cells expressing D^VI can cause maternal sensitisation, so BCSH recommends against using specific reagents sensitive to D^VI for cord samples. This is is because of the risk of the wrong reagent being used for other pre-transfusion samples. 
  • D^VI patients should be typed as D-negative to prevent them from receiving D-positive blood and potentially becoming alloimmunised.
• If manual systems are used for recipient testing, then each sample should be tested in duplicate; either using the same reagent, or a different monoclonal anti-D reagent.
  • Monoclonal anti-D reagents vary widely in their ability to detect weak D and partial D. Hence, if using two reagents, it is recommended that reagents of similar affinity be used to avoid the risks of apparent discrepancy in D typing.
• Potent monoclonal IgM anti-D detects all but the weakest D antigens; retesting on apparently negative samples is hence not usually required for recipients.
• Anti-CDE reagents should not be used.
• If there is a discrepancy in reaction strength between D reagents, or the reaction is not a clear-cut positive, then the decision to investigate further should depend on whether or not the development of anti-D is likely to cause clinical problems.
  • Women of child-bearing potential and patients who are likely to require long-term transfusion should be treated as D-negative until confirmation is obtained.
  • All other patients can be treated as D positive. 
• Patients known to have partial D status should be treated as D negative.

Other Resources:

• BCSH Guideline: Pre-Transfusion Compatability Procedures (2012)