On liver biopsy from a patient with non-alcoholic steatohepatitis (NASH), the NAFLD Activity Score (NAS) is calculated. Which three histological features are scored to calculate NAS, and what NAS threshold is used to diagnose NASH?
- A Steatosis, fibrosis stage, and Mallory-Denk bodies; NAS ≥3 is diagnostic of NASH
- B Steatosis (0-3), lobular inflammation (0-3), and hepatocyte ballooning (0-2); NAS ≥5 is diagnostic of NASH ✓
- C Portal inflammation, bile duct damage, and periportal fibrosis; any score indicates NASH
- D Steatosis, iron deposition, and lobular inflammation; NAS ≥4 is diagnostic of NASH
Explanation
The NAFLD Activity Score (NAS), developed by the NASH Clinical Research Network, quantifies three semiquantitative histological features: steatosis grade (0 = <5%, 1 = 5-33%, 2 = 34-66%, 3 = >66%), lobular inflammation (0 = none, 1 = <2 foci/20x, 2 = 2-4 foci, 3 = >4 foci), and hepatocyte ballooning (0 = none, 1 = few, 2 = many/prominent). Maximum total score is 8. A NAS ≥5 correlates with the diagnosis of NASH (sensitivity and specificity ~60%), while NAS ≤2 is generally diagnostic of NAFL (simple steatosis). Importantly, NAS is a scoring tool for clinical trial enrolment, not an independent histological diagnosis of NASH — fibrosis stage is assessed separately (F0-F4) as it is the strongest predictor of long-term outcome. Fibrosis is not included in NAS calculation.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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