Low-MFI (median fluorescence intensity) pre-transplant DSA (donor specific antibodies) leading to anamnestic antibody mediated rejection in live-related donor kidney transplantation.

"In solid organ transplantation, the compatibility between recipient and donor relies on testing prior to transplantation as a major determinant for the successful transplant outcomes. This compatibility testing depends on the detection of donor-specific antibodies (DSAs) present in the recipient. Indeed, sensitized transplant candidates are at higher risk of allograft rejection and graft loss compared to non-sensitized individuals. Most of the laboratories in India have adopted test algorithms for the appropriate risk stratification of transplants, namely: 1) donor cell-based flow-cytometric cross-match (FCXM) assay with patient's serum to detect DSAs; 2) HLA-coated beads to detect anti-HLA antibodies; and 3) complement-dependent cytotoxicity crossmatch (CDCXM) with donor cells to detect cytotoxic antibodies. In the risk stratification strategy, laboratories generally accept a DSA median fluorescence index (MFI) of 1000 MFI or lower MFI (low-MFI) as a negative value and clear the patient for the transplant. We present two cases of live-related donor kidney transplants (LDKTs) with low-MFI pre-transplant DSA values who experienced an early acute antibody-mediated rejection (ABMR) as a result of an anamnestic antibody response by DSA against HLA class II antibodies. These results were confirmed by retesting of both pre-transplant and post-transplant archived sera from patients and freshly obtained donor cells. Our examples indicate a possible ABMR in patients with low MFI pre-transplant DSA. Reclassification of low vs. high-risk may be appropriate for sensitized patients with low-MFI DSA."