Table 1 The Banff 2013 classification

1. Normal

2. Antibody-mediated

 Acute/active ABMR; all three features must be present for diagnosis

  1. Histologic evidence of acute tissue injury, including one or more of the following:

   Microvascular inflammation (g > 0 and/or ptc > 0)

   Intimal or transmural arteritis (v > 0)

   Acute thrombotic microangiopathy, in the absence of any other cause

  2. Evidence of current/recent antibody interaction with vascular endothelium, including at least one of the following:

   Linear C4d staining in peritubular capillaries (C4d2 or C4d3 by IF on frozen sections, or C4d > 0 by IHC on paraffin sections)

   At least moderate microvascular inflammation ([g +ptc] > 2)

   Increased expression of gene transcripts in the biopsy tissue indicative of endothelial injury if thoroughly validated

  3. Serologic evidence of donor-specific antibodies (DSAs) (HLAor other antigens)

 Chronic, active ABMR; all three features must be present for diagnosis

  1. Morphologic evidence of chronic tissue injury, including one or more of the following:

   Transplant glomerulopathy (TG) (eg > 0), if no evidence of chronic thrombotic microangiopathy Severe peritubular capillary basement membrane multilayering (requires EM)

   Arterial intimal fibrosis of new onset, excluding other causes

  2. Evidence of current/recent antibody interaction with vascular endothelium, including at least one of the following:

   Linear C4d staining in peritubular capillaries (C4d2 or C4d3 by IF on frozen sections, or C4d > 0 by IHC on paraffin sections)

   At least moderate microvascular inflammation ([g +ptc] > 2)

   Increased expression of gene transcripts in the biopsy tissue indicative of endothelial injury, if thoroughly valiated

  3. Serologic evidence of DSAs (HLA or other antigens)

 C4d staining without evidence of rejection; all three features must be present for diagnosis

  1. Linear C4d staining in peritubular capillaries (C4d2 or C4d3 by IF on frozen sections, or C4d > 0 by IHC on paraffin sections)

  2. g = 0, ptc = 0, eg = 0 (by light microscopy and by EM if available), v = 0; no TMA, no peritubular capillary basement membrane multilayering, no acute tubular injury (in the absence of another apparent cause for this)

  3. No acute cell-mediated rejection (Banff 97 type 1A or greater) or borderline changes

3. Borderline changes: ‘Suspicious’ for acute T-cell mediated rejection (may coincide with categories 2 and 5, and 6)

 This category is used when no intimal arteritis is present, but there are foci of tubulitis (t1, t2, or t3) with minor interstitial infiltration (i0, or i1) or interstitial infiltration (i2, i3) with mild (t1) tubulitis

4. T cell mediated rejection (TCMR, may coincide with categories 2 and 5 and 6)

 Acute T-cell mediated rejection (Type/Grade:)

  I A. Cases with significant interstitial infiltration (>25% of parenchyma affected, i2 or i3) and foci of moderate tubulitis (t2)

  I B. Cases with significant interstitial infiltration (>25% of parenchyma affected, i2 or i3) and foci of severe tubulitis (t3)

  II A. Cases with mild to moderate intimal arteritis (v1)

  II B. Cases with sever intimal arteritis comprising >25% of the luminal area (v2)

  III. Cases with ‘transmural’ arteritis and/or arterial fibrinoid change and necrosis of medial smooth muscle cells with accompanying lymphocytic inflammation (v3)

 Chronic active T-cell mediated rejection

  ‘chronic allograft aiteriopathy’ (arterial intimal fibrosis with mononuclear cell infiltration in fibrosis, formation of neo-intima)

5. Interstitial fibrosis and tubular atrophy, no evidence of any specific etiology

 (may include nonspecific vascular and glomerular sclerosis, but severity graded by tubulointerstitial features)

  I. Mild interstitial fibrosis and tubular atrophy (>25% of cortical area)

  II. Moderate interstitial fibrosis and tubular atrophy (26-50% of cortical area)

  III. Sever interstitial fibrosis and tubular atrophy/loss (>50% of cortical area)

6. Other: Changes not considered to be due to rejection-acute and/or chronic

 (For diagnoses see table 14 in (Banff 97 KI -1999:)[15]); may include isolated g, eg, or cv lesions and coincide with categories 2, 3,4, and 5)