Laboratories use different protocols to confirm RhIG-derived passive anti-D and simultaneously exclude other antibodies in pregnant females at delivery.
The following are sample protocols (not all inclusive) with comments. All protocols assume,
- That the patient has received RhIG (this needs to be confirmed);
- That the antibody screen is positive (2+ or less);
- Reactions only occurred in the IAT phase;
- Reactions occurred only with D+ screen cells.
In other words, the following protocols assume that the antibody looks like a relatively weak IgG anti-D consistent with RhIG administration.
Probably the most common protocol is to perform a mini-panel to exclude other antibodies and report "probable passive anti-D due to RhIG administration"; "passive anti-D consistent with recent RhIG administration" or similar.
Some commercial panels indicate which panel cells are useful to rule out other antibodies in the presence of anti-D. A mini-panel of 5-7 carefully selected red cells is typically all that is needed.
2. Full panel
Some labs do a full antibody identification panel to confirm anti-D and exclude other antibodies. This protocol is acceptable, but may be overkill given that the same results can be achieved with fewer red cells.