Impact of the Current versus the Previous Diagnostic Threshold on the Outcome of Patients with Borderline Changes Suspicious for T-cell-mediated Rejection Diagnosed on Indication Biopsies.

Background. Since the borderline changes suspicious for acute Tcell-mediated rejection (BL) category was broadened, there has been a debate regarding the right threshold for tubulitis and interstitial inflammation scores. Methods. We studied a first cohort of 111 patients with BL found on an indication biopsy between 2006 and 2016 and compared those with scores of t1i0 (BLt1i0) to those with higher scores (BL >= t1i1). A second cohort of 56 patients with BL was used for external validation. We used a composite endpoint of death-censored graft failure or doubling of the serum creatinine level postbiopsy. Results. In the first cohort, 68% (75/111) of the BL cases fell in the BLt1i0 group. At 5 years, the occurrence of the composite endpoint was 5% and 14% for BLt1i0 and BL >= t1i1, respectively. In contrast, the endpoint occurred in 5% of nonrejectors and 21% of patients with Tcell-mediated rejection. In the validation cohort, 8% versus 36% of BLt1i0 and BL >= t1i1 reached the endpoint, respectively. Multivariable Cox modeling revealed that BLt1i0 patients had a prognosis similar to that of nonrejectors (adjusted hazard ratio, 0.6; 95% confidence interval, 0.1-2.2; P = 0.40) but better than that of patientswith BL >= t1i1 (hazard ratio, 3.8; 95% confidence interval, 1.3-11.5; P = 0.02). Sensitivity analyses restricted to death-censored graft loss or using time posttransplant as the time of reference provided similar results. Conclusions. In summary, patients with BLt1i0 have a different prognosis to that of BL >= t1i1 patients, which brings into question the current diagnostic thresholds.