Flow cytometry crossmatching (FCXM) in the UNOS Kidney Transplant Registry

1. Among 5,776 transplants reported to the UNOS Scientific Renal Transplant Registry with flow cytometry crossmatch (FCXM) results, 13% had a positive FCXM. The majority (8.8%) had B-cell only reactivity and the remaining 4.2% had T-cell reactivity. 2. Retransplanted patients, females and sensitized patients were more likely to have been FCXM positive than primary transplants, males, or unsensitized patients. 3. A positive FCXM was associated with less than optimal function as evidenced by an increased need for posttransplant dialysis, more grafts that never functioned, longer hospital stays and a higher incidence of rejection. 4. The impact of antibodies detected by FCXM on graft survival was strongest among retransplanted patients (60% 3-year graft survival with a positive FCXM vs 79% with a negative FCXM, p = 0.003), although significant differences were also noted in primary transplants (76% 3-year graft survival with a positive FCXM vs 81% with a negative FCXM, p < 0.001). Class I reactivity generally had a greater impact on survival, although class II antibodies had a deleterious effect as well. 5. Primary transplants across a T+B+ FCXM (n = 187) had a 76% 3-year graft survival rate compared with 74% for 509 T-B+ transplants. Both were significantly lower than the 81% 3-year graft survival rate for 5,017 T-B- FCXM transplants. 6. Retransplants across a T+B+ FCXM (n = 48) had a 60% 3-year regraft survival rate compared with 73% for 118 T-B+ regrafts and 79% when the FCXM was negative when tested against both targets (T-B-, n = 698). 7. Although there is room for improvement in the technique, the FCXM continues to be effective in identifying kidney transplants at risk of early graft failure and of rejection.