BACKGROUND: Avoiding donor specific antibody (DSA) is difficult for sensitized patients. Improved understanding of the risk of low level DSA is needed. METHODS: We retrospectively compared the outcomes of 954 patients transplanted with varied levels of baseline DSA detected by single antigen beads and B flow cytometric crossmatch (XM). Patients were grouped as follows: -DSA/-XM, +DSA/-XM, +DSA/low+XM, +DSA/high+XM, and –DSA/+XM and followed for a mean of 4.1±1.9 years (similar among groups, p=0.49). RESULTS: Death-censored allograft survival was similar in all groups except the +DSA/high+XM group, which was lower at 79.1% versus 96.2% in the –DSA/-XM group (p<0.01). The incidence of chronic antibody mediated rejection (CAMR) based on surveillance biopsy was higher with increasing DSA (8.2% -DSA/-XM, 17.0% +DSA/-XM, 30.6%+DSA/low + XM, and 51.2% +DSA/high+XM, p<0.01), but similar in groups without baseline DSA (8.1% -DSA/-XM vs. 15.4% -DSA/+XM, p=0.19). Having a calculated panel reactive antibody (cPRA) ≥80% was independently associated with CAMR (HR 5.2, p=0.03) even when DSA was undetected at baseline. By 2 years posttransplant, the incidence of CAMR was 19.4% in patients with cPRA ≥80% and undetected DSA and negative XM at baseline. CONCLUSION: Kidney transplantation with low level DSA with or without a low positive XM is a reasonable option for highly sensitized patients and may be advantageous compared to waiting for a negative XM deceased donor. The risk for CAMR is low in patients with no DSA even if the XM is positive. Patients with cPRA≥80% are at risk for CAMR even if no DSA is detected.
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