Background: Protocol biopsies can detect sub-clinical rejection. With declining rates of clinical acute rejection, a systematic review of protocol biopsies can provide clues about other subtle clinical and histological correlates of graft injury.

Methods: A single-center, retrospective analysis was conducted on all 6 month protocol renal TX biopsies performed between 2009- 2014, scored by Banff classification by a single pathologist. Data analysis was performed by correlation, regression and anova, with significant p values <0.05.

Results. 1975 patients were consecutively transplanted over the 5 year period; 1062 patients received 6 month protocol biopsies. The mean recipient age was 50±14.6 yrs; mean donor age was 37.5±14.7 yrs, with 37.4% living donors and a DGF rate of 19.9%. Immunosuppression was predominantly TAC/Steroids/MMF, with ATG (41.5%), Simulect (49.6%), Belatacept (2.9%) or Campath (0.18%) induction. TCMR was detected in 3.4% (36) and AHR in 0.4% (5) cases, though borderline changes were called n 8.7% (96). Blood BK-QPCR was positive in 22.8% (252), but BK nephritis was rare at 1.8% (18). Mild tubular atrophy was often seen (54%; 596), but substantive tubular atrophy (ct>2) was rarely seen (4.4%; 48). Mild inflammation (>i0) was seen in 13.4% (148) and some tubulitis could be noted even in non-atrophic areas (>t0) in 26.9% (297), without meeting Banff criteria for rejection. Peri-tubular capillaritis (ptc>0) was rare at 3.2% (35) and arteriolar hylanosis (ah>0) was seen in 16.9% (186). Patients with inflammation had no differences in mean age, DSA, PRA or NODAT, but significantly correlated with greater decline in GFR between 1 and 24 mo (coeff: 0.21 C.I.(0.2 – 0.43); p:0.03).Patients with tubulitis had higher rates of NODAT and DSA and a significant correlation with worse 2 yr GFR (coeff,0.42 C.I.(0.13 – 0.70); p:0.004), which persisted when corrected for age at tx,donor type and NODAT(coeff:0.53 C.I.(0.21 – 0.86); p:0.001). Drug toxicity (ah) had no impact on graft function.

Conclusions. Protocol biopsy data reveals that Banff confirmed sub-clinical rejection is a very low frequency finding, but even very mild changes of inflammation and tubulitis, currently not factored into Banff scoring for an independent rejection diagnosis, have a substantive impact on downstream graft function. Further analysis is underway to develop a composite protocol biopsy risk score that could be more informative for patient management.

CITATION INFORMATION: Geraedts A, Tavakol M, Vincenti F, Chandran S, Laszik Z, Lee B, Roberts J, Sarwal M. A Systematic Over View of Five Year Results of Serial Protocol Kidney Transplant Biopsies. Am J Transplant. 2016;16 (suppl 3).

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