Background: Identifying specific factors that are predictive of renal allograft functional decline is important toward prolonging graft survival. Few studies have addressed specific histologic diagnoses that may determine long-term quality of graft function in recipients maintained on a steroid-free regimen. While the role of early protocol biopsy in predicting graft outcome is well accepted, the utility of late protocol biopsy is yet to be defined. It is unclear if borderline rejections diagnosed on protocol biopsy carry prognostic significance.

Methods: We studied 160 renal transplants on low dose CNI and mycophenolate, transplanted from 2004 to 2010 and followed up for 48±12 months. 158 recipients had early protocol biopsy at 12 months (T12) and 118 recipients had late biopsy at or beyond 24 months (T24). Biopsies were classified as follows: Transplants with interstitial fibrosis and/or tubular atrophy only (IFTA), normal histology (NML), acute rejection (AR), borderline rejection (BDR). The primary end point was 25% decline in estimated glomerular filtration rate (eGFR).

Results: 102 out of 158 T12 biopsies (64.6%) were NML while AR, BDR and IFTA were diagnosed in 6.3%, 10.8% and 18.3%, respectively. AR and IFTA groups in early biopsy (T12) groups had consistently lower eGFR over 48 months; (42.6 ± 3.4 and 46.1 ± 2.8 ml/min) compared to NML group (52.8 ± 1.8 ml/min) (p<0.01). From 118 T24 biopsies, majority were NML (53.4%); IFTA (23.7%); BDR (13.6%) and AR (9.3%). All three abnormal histology groups had lower eGFR than those with NML histology (p< 0.05). Univariate analysis showed that diagnosis of AR in T24 is more associated with decline of graft function (p=0.006) than those diagnosed in T12 (p<0.08). BDR and IFTA groups were only significant if they were diagnosed in T24 (p=0.01). AR diagnosis was the only independent predictor of early decline in graft function in multivariate regression model.

Conclusion: AR on protocol biopsy was a risk factor for decline in function over time. IFTA alone did not result in graft functional decline in this study. Borderline rejections on late protocol biopsy managed by optimizing immunosuppression resulted in lower quality of graft function at follow up. Early and late protocol biopsies were useful tools to predict long-term graft function.

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