Chokri Ben Lamine: The Hidden Risk of RBC Alloimmunization in SCD, Thalassemia and HSCT
Chokri Ben Lamine, Hematologist at King Faisal Specialist Hospital and Research Center, shared a post on LinkedIn:
”RBC alloimmunization in SCD, thalassemia and HSCT | Why can the antibody screen turn negative?
1/8 Evanescence | The antibody falls below detection
An antibody formed after transfusion or pregnancy can fade over time while immune memory persists. Kidd antibodies (anti-Jkᵃ and anti-Jkᵇ) are classic examples. Retrospective studies found that approximately 25 percent of detected RBC alloantibodies became undetectable within 1 month and approximately 50 percent within 6 months. Re-exposure can trigger a rapid anamnestic response and delayed hemolysis.
2/8 The screening cells may miss the target
A routine screen tests plasma against a small set of reagent RBCs. If those cells lack the target antigen, as can happen with a low-incidence antigen, the screen can be negative while an antiglobulin crossmatch with an antigen-positive unit is incompatible.
3/8 Weak antibodies can react differently across cells and methods
Some antibodies show dosage. A weak anti-Jkᵃ may react with Jk(a plus b minus) cells but weakly or undetectably with Jk(a plus b minus) cells. Gel, solid-phase and tube methods can also differ in sensitivity. When the history and current screen disagree, the reference lab can use selected reagent cells or another method.
4/8 Timing matters, especially after transfusion or HSCT
A sample drawn early in a delayed hemolytic reaction can be negative before the antibody becomes detectable. Repeat testing if suspicion persists. Conditioning and donor engraftment can also change antibody detectability. Keep the historical antibody documented through transplant.
5/8 Yesterday’s anti-Jkᵃ still guides today’s transfusion
Retrieve records from outside hospitals. Select crossmatch-compatible units negative for every current or historical clinically significant alloantibody. For SCD and thalassemia, use prophylactic ABO, RhD/C/c/E/e and K matching. In SCD, obtain an extended antigen profile early, favor genotyping after recent transfusion, and request HbS-negative units. In MDS or aplastic anemia, tailor additional matching with the blood bank.
6/8 Before conditioning, check the donor as well as the units
Recipient anti-Jkᵃ plus Jkᵃ-positive stem cell donor? Jkᵃ-negative transfusions protect the transfused units. The donor’s emerging red cells still carry the target. Review donor antigen typing, compatible inventory for any planned exchange and peri-HSCT support, and the phase-specific ABO plan with transfusion medicine.”
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