Low Rate of Red Blood Cell Alloimmunization Among Transfused Children with Sickle Cell Anemia in Malawi without Pre-Transfusion Screening or Antigen Matching

Introduction: In low-resource settings such as Malawi, red blood cell (RBC) transfusions for children with sickle cell anemia (SCA) are cross-matched only for ABO and RhD antigens. RBC alloimmunization occurs when transfusion recipients receive donor blood with foreign erythrocyte surface antigens, leading to antibody formation, and is common in SCA. Once alloantibodies are formed, future RBC transfusions can lead to life-threatening hemolytic transfusion reactions, resulting in high morbidity and mortality. Most alloantibodies form due to incompatibility with RHD or RHCE antigens. In high-resource settings, matching blood for these antigens using extended phenotyping has markedly reduced the frequency and burden of RBC alloantibody formation in SCA. In sub-Saharan Africa, individuals with SCA have varying degrees of alloantibodies, but country-specific data are limited and transfusion practices that include testing and matching for phenotypes and antibodies are largely absent. Studying alloantibody rates in the Malawi SCA population is crucial due to the added complexity brought by comorbidities such as malaria and malnutrition, which may exacerbate the need for RBC transfusions and increase the risk of alloimmunization.

Methods: Children aged 0-18 years were enrolled from the Kamuzu Central Hospital Sickle Cell Clinic in Lilongwe, Malawi. Inclusion criteria included known SCA and a history of at least one prior transfusion. Blood samples were collected, plasma frozen, then tested for alloantibodies using a standard test tube screening method with a 3-cell Panocell® (Immucor Inc) screening panel. If positive, additional cells were used to identify all clinically relevant antibodies. The package insert was followed for all testing with the modification of using a reduced ratio of 1 drop of plasma to 1 drop of reagent red blood cells, due to a limited available plasma volume. Demographic information was also collected including the participant diagnosis, age, sex, number of prior blood transfusions at enrollment (categories of 1-2, 3-5, 6-10, and over 10), and history of transfusion reactions.

Results: A total of 133 children with SCA were enrolled, with an average age of 8.7 years; 58 were female (44%, with 3 missing data). In this cohort, 39% had a history of 1-2 previous transfusions, 31% had 3-5 transfusions, 10% had 6-10, and 20% had received over 10 transfusions. Screening for RBC alloantibodies was successful in 112 samples, with 21 samples having inadequate volume or missing. A total of 3 samples (2.7%) had an alloantibody detected; one was confirmed for anti-D and another for anti-K, while the third sample showed a positive pattern suggestive of anti-D, anti-C, and anti-K. Most participants had reported at least 1 previous transfusion reaction (72%), with the most common symptom being fever. None of the 3 patients with positive alloantibodies reported any signs or symptoms of previous transfusion reactions.

Conclusion: The RBC alloimmunization rate is low in children with SCA living in Malawi. However, 2 children with anti-D antibodies were identified despite routine RhD-matching of transfused blood units. Transfusion reactions were commonly reported by caregivers, but were non-hemolytic and likely not related to alloimmunization. The low alloimmunization rate may be attributed to small numbers of Caucasian donors and limited genetic diversity among the Malawian blood donor population. The observed anti-D formation may be due to polymorphisms in the D antigen, which have not been well-studied in sub-Saharan Africa. Despite limited pre-transfusion testing, Malawian children with SCA did not have significant negative outcomes from lack of alloantibody screening or phenotype matching. Further studies are needed to understand the antigen frequencies between donors and recipients as well as genetic diversity in the Rh blood groups. Further research into RHCE and RHD genetic polymorphisms is essential for understanding alloimmunization risks, highlighting the need for country-specific data rather than generalizing findings across sub-Saharan Africa.