The clinical significance of flow cytometry crossmatching in heart transplantation

Background: Flow cytometry crossmatching is more sensitive than cytotoxic methods in identifying preformed antibodies to donor alloantigens. However, the significance of a positive flow crossmatch remains unknown for a recipient of a heart transplant who has a negative antihuman globulin crossmatch. Methods: Flow crossmatching was performed retrospectively for 92 recipients of a primary cardiac allograft who underwent transplantation with a negative AHG crossmatch. Results: Forty-six patients were flow crossmatch-positive for alloantibody: 20 were positive on both T and B lymphocytes, 12 were positive only on B lymphocytes, and 13 were positive only on T lymphocytes. Eleven had autoantibody invalidating the flow crossmatch with donor cells. Thirty-six patients had negative flow crossmatch, A significantly higher incidence of graft dysfunction with vascular rejection by 6 months was found for patients who had a positive flow crossmatch on B lymphocytes. This group also had an increased incidence of mortality within this same period. Patients who were flow crossmatch-positive on T and B lymphocytes were more likely to experience greater than two episodes of treated cellular rejection within the first 6 months. Flow crossmatch-positive patients stayed longer in the hospital in comparison to the other two groups, although the increases were not statistically significant. There were no differences between groups with regard to time to first rejection, absence of rejection episodes, episodes of decreased cardiac index (<2.3 L/m(2)), depressed left and right ventricular ejection fraction, or development of transplant atherosclerosis. Conclusion: A positive flow crossmatch identified a subset of patients who are predisposed to development of vascular rejection or are more likely to have frequent cellular rejection.