A scenario where anti-D is detected at delivery in a patient who received RhIG during pregnancy raises the question, is the anti-D active or passive?
Distinguishing between passive and immune anti-D is important clinically:
- If passive anti-D is misinterpreted as active, RhIG prophylaxis may be omitted, leading to D sensitization.
- If active anti-D is misinterpreted as passive, appropriate antibody investigation may be curtailed putting the fetus at risk of developing HDFN.
When this occurs, two main serologic questions need to be answered:
- Are the reactions due to passive anti-D from RhIG or due to active anti-D?
- Are there other antibodies that need to be excluded?