Value of a flow cytometry cross-match in the setting of a negative complement-dependent cytotoxicity cross-match in heart transplant recipients.

Complement-dependent cytotoxicity cross-match (CDCXM) is used for evaluation of preformed HLA-specific antibodies in patients undergoing heart transplantation. Flow cytometry cross-match (FCXM) is a more sensitive assay and used with increasing frequency. To determine the clinical relevance of a positive FCXM in the context of negative CDCXM in heart transplantation, the United Network for Organ Sharing (UNOS) database was analyzed. Kaplan-Meier analysis and Cox proportional hazard modeling were used to assess graft survival for three different patient cohorts defined by cross-match results: T-cell and B-cell CDCXM+ ("CDCXM+" cohort), CDCXM- but T-cell and/or B-cell FCXM+ ("FCXM+" cohort), and T-cell/B-cell CDCXM- and FCXM- ("XM-" cohort). During the study period, 2558 patients met inclusion criteria (10.7% CDCXM+, 18.8% FCXM+, 65.5% XM-). CDCXM+ patients had significantly decreased graft survival compared to FCXM+ and XM- cohorts (P = .003 and <.001, respectively). CDCXM- and FCXM+ patients did not have decreased graft survival compared to XM- patients (P = .09). In multivariate analysis, only CDCXM+ was associated with decreased graft survival (HR 1.22, 95% CI 1.01-1.49). In conclusion, positive FCXM in the context of negative CDCXM does not confer increased risk of graft failure. Further study is needed to understand implications of CDCXM and FCXM testing in heart transplant recipients.