Red blood cell alloantibodies in the context of critical bleeding and massive transfusion

In the context of critical bleeding and massive transfusion (CB/MT), little is known about the development of new red blood cell (RBC) alloantibodies. We performed a retrospective, observational study to examine the frequency of RBC alloantibodies (pre-existent, anamnestic, or new) in patients with CB/MT, defined as transfusion of five or more RBC units in any 4-hour period, for any cause of CB.

Data on 2,585 New Zealand patients (date/time of MT initiation, demographic data, blood group, clinical context, and transfused RBCs) were obtained from the Australian and New Zealand Massive Transfusion Registry. RBC alloantibody screening/identification data were extracted from the New Zealand Blood Service database. We calculated summary statistics, compared proportions between different independent groups using the Chi-squared test, and performed logistic regression analysis to examine the effects of variables on alloantibody presence or formation. We also determined the immunogenicities of selected RBC antigens in the context of CB/MT.

Of 1,234 assessable patients, 1,166 (94.5%) showed no evidence of any alloantibody. Pre-existent, anamnestic, and new alloantibodies were found, respectively, in 4.3%, 0.4%, and 7.2% of assessable patients. By multivariable regression analysis, transfusion of D-positive RBC to D-negative patients was independently associated with new alloantibody formation. Neither the quantum of RBC transfused nor trauma as clinical context were so associated although the latter trended towards a predisposition. "Antibodies of undetermined specificity" were the commonest pre-existent and new alloantibodies. The immunogenicity of Jk^a was the highest in this setting.

RBC alloantibodies of any type were rare in this CB/MT population. Patients undergoing CB/MT appear to have low risks of re-stimulating anamnestic alloantibodies, or of developing new RBC alloantibodies.