Incompatibility Between Group O Patient and Group O Blood Bags
The most likely cause is ABO antibody-related incompatibility in the donor blood bags, specifically high-titer anti-A or anti-B antibodies in the group O donor plasma that are reacting with the patient's red cells during compatibility testing, or the presence of unexpected alloantibodies in either the patient or donor units.
Primary Causes to Investigate
High-Titer Anti-A/Anti-B in Donor Plasma
- Group O donors naturally produce anti-A and anti-B antibodies, but some donors have unusually high titers that can cause positive crossmatch reactions 1, 2, 3
- The two incompatible bags likely contain high-titer anti-A or anti-B antibodies that are reacting during the major crossmatch, even though both donor and recipient are group O 4
- This phenomenon is well-documented: anti-A/B titers >100 (saline) or >400 (antiglobulin) significantly increase incompatibility risk 4
Unexpected Red Cell Alloantibodies
- The patient may have developed alloantibodies from previous transfusions, pregnancy, or transplantation that are reacting with antigens present on the two incompatible donor units but absent on the compatible unit 5, 6
- Common culprits include antibodies to Rh antigens (D, C, E, c, e), Kell, Duffy, Kidd, or other minor blood group systems 6
- One case report documented hemolytic transfusion reaction from reactivation of anamnestic JK antibodies in a trauma patient 6
Technical or Clerical Issues
- Verify that all three bags are truly group O through repeat ABO typing 2
- Sample validity: compatibility testing samples are valid for only 72 hours (3 calendar days) for patients without recent transfusion or pregnancy history 2
- Human error in labeling or testing is a recognized cause of apparent incompatibility 2
Immediate Actions Required
Work with Blood Bank
- Request extended phenotyping of all three donor units and antibody screening/identification panel on patient serum 5
- Perform direct antiglobulin test (DAT) on patient's red cells to detect coating antibodies 7
- Use at least two different serological methods to confirm findings and ensure concordance 5
Clinical Context Matters
- Review patient's transfusion history: previous transfusions increase alloimmunization risk 6
- Check for pregnancy history in female patients: up to 30% of multiparous women develop anti-HLA antibodies 5
- Assess for recent immunization events (vaccination, transplantation) that could trigger antibody formation 4
Critical Pitfalls to Avoid
- Do not assume all group O blood is universally compatible - antibody titers and minor antigens matter 1, 2, 3
- Do not proceed with transfusion of the incompatible units - risk of acute hemolytic transfusion reaction with potential for disseminated intravascular coagulation, acute kidney injury, and death 7
- Do not delay investigation: false-negative antibody tests can occur with low-affinity or delayed antibodies that appear weeks after sensitization 5
Resolution Strategy
The blood bank should identify the specific antibody causing incompatibility through extended testing, then provide antigen-negative blood for transfusion 5. If alloimmunization is confirmed, all future transfusions must be phenotypically matched to avoid the implicated antigen 5. The compatible bag #3 can be used while investigation proceeds, assuming it remains within the 72-hour validity window 2.