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Staging and Grading Disease Activity in Steatohepatitis

Histological Scoring System for Nonalcoholic Fatty Liver Disease

Components of NAFLD Activity Score (NAS) and Fibrosis Staging

Nonalcoholic Steatohepatitis Clinical Research Network

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.
	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	"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)
Item	Score	Extent	Definition and Comment
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
Scoring interpretation: 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

Reference: Kleiner D.E., Brunt E.M., Van Natta M., Behlinh C., Contos M.J., Cummings O.W., Ferrell L.D., Liu Y.-C., Torbenson M.S., Unalp-Arida A., Yeh M., McCullough A.J., Sanyal A.J. for the Nonalcoholic Steatohepatitis Clinical Research Network. Design and validation of a histological scoring system for nonalcoholic fatty liver disease. Hepatology 41:1313-1321, 2005.

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