Ahmed Abdelsalam: Why Matching ABO and RhD Groups Does Not Guarantee Crossmatch Compatibility
Ahmed Abdelsalam, Medical Laboratory Technician at Bir al-Abd, shared a post on LinkedIn:
“Same ABO and Rh group, yet the crossmatch is incompatible.
Why?
It happens more often than people expect, and the answer is a core concept in transfusion medicine: matching ABO and RhD does not guarantee compatibility.
Common causes:
1. Unexpected red cell antibodies
- The patient’s plasma may contain antibodies against other antigens, such as Kell, Duffy, or Kidd.
2. Autoantibodies
- Antibodies against the patient’s own red cells can cause positive reactions during compatibility testing.
3. Previous transfusion or pregnancy
- Past exposure can lead to alloantibodies. Even when levels fall below detection, re-exposure can trigger a rapid secondary response.
4. Rouleaux
- High protein levels, for example in myeloma, can mimic agglutination.
5. Cold antibodies
- Cold agglutinins may react at room temperature.
6. Drug interference
- Some therapies, such as daratumumab, can interfere with testing.
7. Technical or clerical error
- Wrong sample, labeling mistakes, or wrong dilution.
Blood grouping tells us the ABO and RhD type.
Crossmatching tells us whether this donor’s red cells are compatible with this patient’s plasma.
In transfusion medicine, compatibility is more than just a blood group.
Your incompatible crossmatch has identical ABO/RhD groups.
What do you check first?
A) Sample and unit identification
B) Antibody screen
C) DAT
D) Repeat the test”
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