Histological Scoring System for Nonalcoholic Fatty Liver Disease (NAFLD)

Components of NAFLD Activity Score (NAS) and Fibrosis Staging

NAS Components (see scoring interpretation)
Item Score Extent Definition and Comment
Steatosis 0 <5% Refers to amount of surface area involved by steatosis as evaluated on low to medium power examination; minimal steatosis (<5%) receives a score of 0 to avoid giving excess weight to biopsies with very little fatty change
1 5-33%
2 >33-66%
3 >66%
Lobular Inflammation 0 No foci Acidophil bodies are not included in this assessment, nor is portal inflammation
1 <2 foci/200x
2 2-4 foci/200x
3 >4 foci/200x
Hepatocyte Ballooning 0 None
1 Few balloon cells The term “few” means rare but definite ballooned hepatocytes as well as cases that are diagnostically borderline
2 Many cells/prominent ballooning Most cases with prominent ballooning also had Mallory’s hyalin, but Mallory’s hyaline is not scored separately for the NAS


Fibrosis Stage (Evaluated separately from NAS)

Fibrosis 0 None
1 Perisinusoidal or periportal
1A Mild, zone 3, perisinusoidal “delicate” fibrosis
1B Moderate, zone 3, perisinusoidal “dense” fibrosis
1C Portal/periportal This category is included to accommodate cases with portal and/or peri portal fibrosis without accompanying pericellular/perisinusoidal fibrosis
2 Perisinusoidal and portal/periportal
3 Bridging fibrosis
4 Cirrhosis

Total NAS score represents the sum of scores for steatosis, lobular inflammation, and ballooning, and ranges from 0-8. Diagnosis of NASH (or, alternatively, fatty liver not diagnostic of NASH) should be made first, then NAS is used to grade activity. In the reference study, NAS scores of 0-2 occurred in cases largely considered not diagnostic of NASH, scores of 3-4 were evenly divided among those considered not diagnostic, borderline, or positive for NASH. Scores of 5-8 occurred in cases that were largely considered diagnostic of NASH.




  1. Kleiner DE, Brunt EM, Van Natta M, Behling C, Contos MJ, Cummings OW, Ferrell LD, Liu YC, Torbenson MS, Unalp-Arida A, Yeh M, McCullough AJ, Sanyal AJ; Nonalcoholic Steatohepatitis Clinical Research Network. Design and validation of a histological scoring system for nonalcoholic fatty liver disease. Hepatology. 2005 Jun;41(6):1313-21. [Medline]

Created: May 11, 2007