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:
-
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]
