Nomenclature and Grading of Liver Allograft Rejection (NIDDK-LTD)
Acute Rejection*
Grade	Histopathological Findings
A0 (None)	No rejection
A1 (Mild)	Rejection infiltrate in some, but not most, of the triads, confined within the portal spaces
A2 (Moderate)	Rejection infiltrate involving most or all of the triads, with or without spillover into lobule. No evidence of centrilobular hepatocyte necrosis, or dropout
A3 (Severe)	Infiltrate in some or all of the triads, with or without spillover into the lobule, with or without inflammatory cell linkage of the triads, associated with moderate-severe lobular inflammation and lobular necrosis and dropout
* The diagnosis of acute rejection is based on the presence of at least two of the following three findings: 1) predominantly mononuclear but mixed portal inflammation; 2) bile duct inflammation/damage; and 3) subendothelial localization of mononuclear cells in the portal or central veins. Thereafter, the severity of rejection was graded on the above findings.
Chronic (Ductopenic) Rejection§
Grade	Histopathological Findings
B1 (Early or Mild)	Bile duct loss, without centrilobular cholestatis, perivenular sclerosis, hepatocyte ballooning or necrosis and dropout
B2 (Intermediate/moderate)	Bile duct loss, with one of the following four findings: centrilobular cholestasis, perivenular sclerosis, hepatocellular ballooning, necrosis and dropout
B3 (Late or severe)	Bile duct loss, with at least two of the following four findings: centrilobular cholestasis, perivenular sclerosis, hepatocellular ballooning, centrilobular necrosis and dropout
§ Bile duct loss in > 50% of triads must be present for the diagnosis.
Reference Demetris AJ, et al. Reliability and Predictive Value of the National Institute of Diabetes and Digestive and Kidney Diseases Liver Transplantation Database: Nomenclature and Grading System for Cellular Rejection of Liver Allografts. Hepatology 1995;21(2):408-16.