Banff borderline: where do we stand?

Banff borderline is a category 3 diagnostic entity in Banff classification scheme for histological diagnosis of kidney allografts. The biopsies with borderline changes have i score or percentage of interstitial mononuclear cell infiltrate in non-scarred area not more than 25% (i0 or i1) and any degree of tubulitis (t1, t2, t3). Becker et al. surveyed renal pathologists worldwide and found that the majority of them reserved the diagnosis for borderline changes for biopsies with i1 or 10-25% interstitial infiltrate. They did not consider biopsies with i0 to be in borderline category. Interestingly, many of them admitted to exaggerate i score in order to meet the diagnosis of borderline.

Eliminating borderline rejection

According to Banff classification, borderline rejection in kidney allografts exist as an entity between no acute rejection and acute cellular or T cell-mediated rejection type IA. Its criteria were arbitrarily set with mild tubulitis (t score equal to or less than 1) and/or mild interstitial mononuclear cell infiltrate (i score equal to or less than 1). Borderline rejection is problematic because it does not tell whether rejection is occurring in the grafts. Acute tubular necrosis, a common cause of delayed graft function, can also have similar histologic features.