Laboratories use different protocols to confirm anti-D from RhIg administration and simultaneously exclude other antibodies in pregnant females at delivery.
The following protocols are examples only and assume:
- That the patient received RhIg (this needs to be confirmed)
- That the antibody screen is positive (2+ or less)
- Antibody reacts only in the IAT phase and 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.
Antibody Exclusion Protocols
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.
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.
Passive versus immune
Unfortunately, there is no definitive test to determine if anti-D is passive or immune. Some labs perform a titration with the assumption that an anti-D titer greater than 4 likely
represents active immunization. While a high titer can exclude passive anti-D, a low titer cannot.
This issue is discussed in detail in Rh Negative Female with Anti-D at Delivery: A Case Study on Dealing with the Issues, a case study that complements this course.