Banff '07 Criteria Reviewed

Trick question:  where was the 9th Banff Conference on Allograft Pathology in 2007 held?  Hint:  it wasn't Banff (the beautiful national park in western Canada).  Answer:  La Coruna, Spain.  At this conference a consensus regarding the histopathologic classification of renal transplant biopsies was made and exists as an updated form of the so-called "Banff Criteria."  It is currently the most widely-used scoring system for describing renal allograft biopsies.  

The full scoring system along with commentary can be found in this paper published in a 2008 issue of the American Journal of Transplantation.  As I wanted to review this prior to taking my ASN in-service exam tomorrow, I'll write out the salient details of the Classification system.

Class 1 is a "normal biopsy." 

Class 2 is "antibody-mediated changes."  Ideally, both positive C4d staining and circulating donor-specific antibodies are present in the setting of a rising creatinine to make this diagnosis.  In acute antibody-mediated rejection, there are three variants:  (i) an ATN-like picture, (ii) capillary involvement, or (iii) arterial involvement.  In chronic antibody-mediated rejection, there is evidence of chronic tissue injury such as glomerular double contours, peritubular capillary basement membrane multilayering, interstitial fibrosis/tubular atrophy (IFTA), or fibrous intimal thickening in arteries.

Class 3 refers to "Borderline Changes" which is essentially a mild form of T-cell-mediated rejection.  This category is used when there is no intimal arteritis present, but there are foci of tubulitis or minor interstitial infiltration.

Class 4 is a more full-blown form of T-cell mediated rejection.  As with humoral rejection, there are both acute & chronic forms:

The acute form of T-cell mediated rejection is furthermore subclassified as follows.  Since this is the most common form of rejection, it is useful to know:

Class IA: there is at least 25% of parenchymal showing interestitial infiltration and foci of moderate tubulitis (defined as a certain number of immune cells present in tubular cross-sections).  

Class IB:  just like Class IA except there is more severe tubulitis.

Class IIA:  there is mild-to-moderate intimal arteritis.

Class IIB:  there is severe intimal arteritis comprising at least 25% of the lumenal area.

Class III:  there is transmural (e.g. the full vessel wall thickness) arteritis.

Class 5 refers to interstitial fibrosis and tubular atrophy (IFTA), which is the new preferred term for "chronic allograft nephropathy."  Grade I refers to <25%>50% of cortical area involved.

Class 6 is a catch-all term describing changes not considered to be due to rejection--for example, recurrent FSGS or CNI toxicity.