Evolving thresholds for the diagnosis of acute T cell mediated rejection

The Banff schema uses combinations of pathological lesions at predefined thresholds to diagnose of T cell rejection (TCMR) and grade its severity. Constant definitional changes have caused confusion among clinicians and pathologists. This review describes the evolution of lesion definitions and the rationale for the minimal thresholds.

The minimal diagnostic threshold for borderline TCMR has been reset to original Banff i1/t1, where isolated tubulitis is now excluded. Arteritis can be mediated by either Grade II TCMR or caused by donor specific antibody as antibody-mediated vascular rejection. The conservative threshold for chronic active TCMR diagnosis uses moderate total and scarred inflammation with tubulitis has been challenged by recent longitudinal data to suggest lower thresholds including i-IFTA=1 as clinically relevant.

Minor changes in the threshold ruleset can cause substantial alterations in the final pathological diagnoses. While minimal thresholds for borderline and active TCMR have now stabilized, future changes are likely for chronic active TCMR pending confirmatory research.