[Dynamic and flexible classification of transplant rejection]

Different classification systems of renal allograft rejection are in use. Although, significant progress has been made with the introduction of the widely recognized Banff classification scheme, major problems remain unsolved. Minimal diagnostic threshold levels for tubulo-interstitial rejection are lacking. "Hyperacute, acute and chronic rejection or allograft nephropathy" are ill defined entities and thereby hamper rather than promote the communication between clinicians and pathologists and prevent a better understanding of pathophysiological events. Here, we propose a classification system of renal allograft rejection which is primarily based on well characterized morphological changes. All anatomical compartments of the renal cortex i.e., the tubulo-interstitial compartment, arteries and glomeruli, can be affected by rejection individually or in combination. In the subgroups only morphological changes known to be induced by rejection are considered. Such a classification system has, in our opinion, several major advantages. Every group and subgroup can easily be amended by "qualifiers" providing additional immunohistochemical and molecular-biological information as they are known today or become available in the future. As knowledge expands, qualifiers may be added or removed without fundamentally changing the entire classification scheme--making the system flexible and dynamic.