P064 Serum treatment in a flow crossmatch

Abstract

Aim Autoantibodies present in patient sera may cause a positive flow cytometric crossmatch that is not clinically relevant. Previous studies have shown that pronase treatment of lymphocytes reduces autoreactivity. However, in addition to removing Fc receptors, treatment with pronase can affect HLA antigen expression. More recent studies show that pronase treatment can also create cryptic epitopes, and many laboratories that treat unseparated T and B cells have reported an increased incidence of positive T cell and negative B cell crossmatches. For these reasons, our laboratory has focused on treatment of serum to enhance assay performance. Hypotonic dialysis (HD) is one of many serum treatments that are used to reduce non-specific reactivity. In this study we assess the ability of HD treatment to remove autoantibodies and improve the specificity of the flow crossmatch. Method We identified T cell ( n = 68) and B cell crossmatches ( n = 56) performed between January 2015 and May 2016 in which untreated and hypotonically dialyzed (HD) sera were used to perform an autologous crossmatch. The crossmatch was considered positive if the test serum to negative control ratio was ⩾2.5. Results There was a significant decrease in the ratio of HD compared to untreated sera in B cell autocrossmatches (mean ratio 1.16 versus 1.76; p = 0.002) and no significant difference between with the T cell autocrossmatches (mean ratio 1.05 versus 1.1; p = 0.06). Eleven (19%) B cell autocrossmatches were positive with the untreated serum (mean ratio 3.5 versus 1.8 for the HD; p = 0.005). Four autocrossmatches (7%) remained positive with HD serum. Conclusion Hypotonic dialysis reduced auto-reactivity in B cell autocrossmatches. Treatment of sera to remove interference offers several advantages; the same serum can be used in solid-phase immunoassays, an untreated serum can be used as a control and most importantly it maintains integrity of lymphocytes used in the crossmatch.