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.

 

 

References:

  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