In vitro studies of the impact of transfusion on the detection of alloantibodies after autoadsorption

BACKGROUND: In a patient with warm autoantibodies who has recently received a transfusion, it is not recommended to perform adsorptions using autologo us RBCs to detect alloantibodies. Although not scientifically documented, t his position is based on the theory that transfused RBCs in the patient's c irculation would be capable of adsorbing alloantibodies that may be present . This in vitro study was designed to determine what percentage of transfus ed RBCs might completely remove alloantibodies in vivo. STUDY DESIGN AND METHODS: Selected D, E, K, Fy(a), and Jk(a) antibodies wer e adsorbed with mixtures of antigen-positive and antigen-negative RBCs to d etermine the lowest concentration of antigen-positive RBCs capable of remov ing all alloantibody reactivity. The percentage of antigen-positive RBCs in each mixture was determined by flow cytometry. RESULTS: Small amounts of antigen-positive RBCs (2-6%, as determined by flo w cytometry) completely removed anti-D, -E, and -Fy(a) reactivity. Reactivi ty of two examples of anti-K was removed by 11 percent and -17 percent of K + RBCs, respectively Anti-Jk(a) reactivity was completely removed by 4 to 5 percent Jk(a+) RBCs using a PEG adsorption; the endpoint (>11%) was estima ted, hut complete adsorption with ZZAP-treated RBCs was not performed. CONCLUSION: Small amounts of antigen-positive RBCs are generally capable of removing all alloantibody reactivity. Thus, waiting for 3 months after tra nsfusion before performing autologous adsorptions is a prudent policy.