Evolution of human kidney allograft pathology diagnostics through 30 years of the Banff classification process

Table 1 Adequacy criteria of renal allograft biopsies for an accurate pathologic diagnosis

Parameters/investigations	Requirements
Number of cores	Two (these should be divided to procure tissue for IF and EM studies, if necessary)
Components of graft parenchyma	Both cortex and medulla
For the light microscopic study	A significant amount of cortex containing up to: (1) 10 glomeruli; and (2) 2 arteries
For the immunofluorescence study	Cortex with up to 3 glomeruli
For the electron microscopic study	Cortex with 1 glomerulus

EM: Electron microscopy; IF: Immunofluorescence.

Table 2 Banff reporting standardization template according to the Banff 2019 meeting

Components of the allograft	Acute lesions	Scoring as 0, 1, 2, 3	Chronic lesions	Scoring as 0, 1, 2, 3	Acute & chronic lesions	Scoring as 0, 1, 2, 3
Glomeruli	g	-	cg	-
Interstitium	i	-	ci	-	ti, i-IFTA	-
Tubules	t	-	ct	-	t-IFTA	-
Vessels	v	-	cv	-
Peritubular capillaries	ptc	-	ptcml	-
C4d	C4d	-

C4d: Linear staining in peritubular capillaries or medullary vasa recta either by immunofluorescence on frozen sections of fresh frozen tissue or immunohistochemistry on formalin-fixed, paraffin-embedded tissue; cg: Chronic glomerulopathy (transplant glomerulopathy); ci: Interstitial fibrosis involving the cortex; ct: Tubular atrophy in the cortex; cv: Arterial intimal fibrosis (fibrointimal thickening); g: Glomerulitis; i: Inflammation in the non-scarred cortex; i-IFTA: Inflammation in the scarred cortex; ptc: Peritubular capillaritis; ptcml: Peritubular capillary basement membrane multilayering (requires EM for detection); t: Tubulitis in cortical tubules within the non-scarred cortex; ti: Total cortical inflammation, including scarred and non-scarred cortex; t-IFTA: Tubulitis in mildly to moderately atrophic tubules within the scarred cortex; v: Arteritis (intimal to transmural arteritis).

Table 3 Main changes in the nomenclature and classification of antibody-mediated rejection in the Banff classification over three decades of evolution (1991 to 2019)

Meeting reports, year	Category 2: Antibody-mediated rejection1
Banff, 1993	Hyperacute rejection
Banff, 1997	AMR3
	Hyperacute
	Accelerated acute3
Banff, 1997 update (2001)	Diagnostic criteria for acute antibody-mediated rejection were developed. Three types were described as: (1) Types I: ATN-like3; (2) Types II: Capillary3; and (3) Type III: Arterial3
Banff, 2005	Diagnostic criteria for chronic antibody-mediated rejection were developed
Banff, 2007	Antibody-mediated changes2,3
	C4d deposition without rejection3
	Acute antibody-mediated rejection
	Chronic active3 antibody-mediated rejection
Banff, 2013	Antibody-mediated changes
	Acute/active antibody-mediated rejection
	Chronic active antibody-mediated rejection
	C4d-negative antibody3-mediated rejection
Banff, 2015	Antibody-mediated changes
	Acute/active3 antibody-mediated rejection
	Chronic active antibody-mediated rejection
	C4d staining without evidence of rejection
	Transplant arteriopathy may be seen in chronic AMR
Banff, 2017	Antibody-mediated changes
	Active3 AMR
	Chronic active AMR
	C4d staining without evidence of rejection
	3 criteria for AMR diagnosis remain but C4d can substitute for DSA
	DSA testing still advised
	Suspicious for AMR eliminated
Banff, 2019	Category 2: Antibody-mediated changes
	Active AMR
	Chronic active AMR
	Chronic (inactive) AMR3
	C4d staining without evidence of rejection

¹May coincide with categories 3, 4 and 5 and 6;

²With the identification of c4d positivity without rejection, the category name was changed from rejection to changes);

³Changes in the nomenclature or criteria. AMR: Antibody-mediated rejection; ATN: Acute tubular necrosis; DSA: Donor-specific antibody.

Table 4 Main changes in the nomenclature and classification of T cell-mediated rejection in the Banff classification over three decades of evolution (1991 to 2019)

Meeting reports, year	Category 4: T cell-mediated rejection1
Banff, 1993	Acute rejection, grades I, II, III
Banff, 1997	Acute/ active cellular rejection
	Types2 I A/B, II A/B, III
Banff, 1997 update (2001)	Acute/ active cellular rejection
	Types I A/B, II A/B, III
Banff, 2005	TCMR2
	Acute, types2 I A/B, II A/B, III
	Chronic active2 (includes only transplant arteriopathy)
Banff, 2007	TCMR
	Acute
	Chronic active (includes only transplant arteriopathy)
Banff, 2013	TCMR
	Acute
	Chronic active (includes only transplant arteriopathy)
Banff, 2015	TCMR
	Acute
	Chronic active TCMR may have tubulointerstitial changes2
Banff, 2017	TCMR
	Acute
	Chronic active TCMR grades I A/B and II defined
Banff, 2019	i-IF/TA and t-IF/TA included in criteria2 (inflammation and tubulitis in areas of scarring)
	In chronic active TCMR with i >1, diagnosis to be combined chronic active and acute TCMR2

¹May coincide with categories 3, 4 and 5 and 6;

²Changes in the nomenclature or criteria. i-IFTA: Inflammation in the scarred cortex; TCMR: T cell mediated rejection; t-IFTA: Tubulitis in mildly to moderately atrophic tubules within the scarred cortex.

Table 5 Main changes in the nomenclature and classification of chronic changes of the allograft in the Banff classification over three decades of evolution (1991 to 2019)

Meeting reports, year	Category 5: Chronic allograft nephropathy
Banff, 1993	CAN, grades, I, II, III
Banff, 1997	CAN, grades, I, II, III, each divided into a and b subcategories1
Banff, 1997 update (2001)	CAN, grades, I, II, III, a and b
Banff, 2005	IFTA, of no specific etiology1, grades I, II, III
Banff, 2007	IFTA of no specific etiology, grades I, II, III
Banff, 2013	IFTA of no specific etiology, grades I, II, III
Banff, 2015	IFTA of no specific etiology, grades I, II, III
Banff, 2017	IFTA of no specific etiology, grades I, II, III
Banff, 2019	Grading of polyoma viral nephropathy into classes 1, 2 and 3 (adequate sampling for scoring should include 2 cores with medulla)1

¹Changes in the nomenclature or criteria. CAN: Chronic allograft nephropathy; IFTA: Interstitial fibrosis/tubular atrophy.