Evaluation of methods for detecting alloantibodies underlying warm autoantibodies

BACKGROUND: In pretransfusion testing of patients whose sera contain autoan tibodies reacting optimally at 37 degrees C, it must be determined whether alloantibodies are also present. Two approaches, testing a 1-in-5 dilution of patients' sera and the adsorption of sera in the presence of polyethylen e glycol (PEG), have been proposed as alternatives to the time-consuming ap proach of adsorbing sera with ficin- or ZZAP-treated red cells (RBCs). The three approaches were compared. STUDY DESIGN AND METHODS: Patients' sera containing warm autoantibodies, wi th and without alloantibodies, were retested 1) after dilution (1-in-5) and 2) after adsorption with allogeneic RBCs in the presence of PEG. Results w ere compared to those after adsorption with ZZAP-treated allogeneic RBCs. RESULTS: Dilution (1-in-5): Twenty-seven of 119 sera (7/26 [27%] with and 2 0/93 [22%] without alloantibodies) did not react; one example each of alloa nti-D, -E, -e, - Fy(a), and -Jk(a), and two examples of anti-Jk(b) were not detected at a dilution of 1 in 5. Alloantibodies were identified in 5 (19% ) of 26 1-in-5 diluted sera containing alloantibodies; 87 (73%) of 119 sera still reacted with all cells and would have required further workup. PEG a dsorption: Thirty-nine sera were tested after parallel PEG and ZZAP adsorpt ions. The PEG adsorptions required a total of 55 aliquots of adsorbing cell s and 13.75 hours, whereas ZZAP adsorptions required 61 aliquots and 30.5 h ours. All alloantibodies (anti-D [3], -C [2], -e [1], -E [4], -K [2], -Fy(a ) [1], -Jk(a)[2], -Jk(b)[1]) reacted in the adsorbed serum-PEG mixtures at a strength equal to or greater than that in the ZZAP-adsorbed sera. CONCLUSION: Although the 1-in-5 dilution approach is convenient, only 22 pe rcent of warm autoantibodies without alloantibodies were nonreactive, and 2 7 percent of alloantibodies of potential clinical significance were not det ected. PEG adsorption appears to give similar results to those of ZZAP adso rption, but it has the advantages of eliminating the cost and time of prior treatment of the allogeneic adsorbing cells and of a reduction of at least a 50 percent in adsorption time.