P133 A reappraisal of the impact of heat inactivation of kidney graft recipient’s serum on donor T cell and B cell CDC crossmatches: An analysis of 22175 consecutive crossmatches performed by a single histocompatibility laboratory

Aim Interfering factors in sera may confound crossmatch (XM) results. Heat inactivation (HI), DTT and dialysis treatment of sera have been utilized to minimize these confounders. We investigated the impact of HI on donor T cell complement dependent cytotoxicity (CDC) XM (T Cell AHG XM) and donor B cell CDC XM (B Cell NIH XM). Methods We queried our electronic database for all donor CDC T cell and B cell XM performed during 2011–2017 in which potential kidney transplant recipient’s serum was tested in parallel with or without HI and using potential donor’s T cells and B cells as target cells. Results A total of 6295 living donor XMs and 15880 deceased donor XMs performed in our laboratory were reviewed. Table 1 shows the impact of HI on the 22175 consecutive XM results. 394 of the 6295 living donor T Cell AHG XMs were positive using neat sera and 303 were positive following HI at 63C for 6 min, a 23% conversion from positive to negative results. 698 of the 15880 deceased donor T Cell AHG XMs were positive using neat sera and 540 XMs were positive following HI, a 23% reduction. 1372 of the 6295 living donor B Cell NIH XMs were positive using neat sera and 539 were positive following HI, a 61% reduction. 3015 of the 15880 deceased donor B Cell NIH XMs were positive using neat sera and 842 XMs were positive following HI, a 72% reduction from a positive result to negative result. Conclusions A substantial percentage of XMs are converted from a positive CDC result to negative result and such conversion is more frequent with B cell XM compared to T cell XM. Transplant centers seldom transplant across a positive T cell CDC XM even when HI converts a positive result to a negative result. On the other hand, it is not uncommon to proceed with a kidney transplant when HI converts a positive B cell CDC to a negative CDC provided there are no other immune contraindications. There is an urgent need to establish the clinical significance of XMs converted from a positive to a negative result by heat inactivation.