gastroenterology & hepatologyformula

NAFLD Fibrosis Score (NFS)

The NAFLD Fibrosis Score is a non-invasive composite score predicting advanced liver fibrosis (F3–F4) in patients with NAFLD/MASLD. It uses age, BMI, diabetes status, AST/ALT ratio, platelets, and albumin.

inputs

years
kg/m²
×10⁹/L

✓ when to use

Use as a non-invasive fibrosis screening tool in patients with confirmed or suspected NAFLD/MASLD, either as an alternative or complement to FIB-4. Particularly useful when a more comprehensive assessment than FIB-4 alone is desired. Can be used as a second-line test after an indeterminate FIB-4.

✗ when not to use

Not validated outside of NAFLD/MASLD (do not use for viral hepatitis or alcoholic liver disease fibrosis assessment). The indeterminate zone captures ~25% of patients who need further testing. Age and BMI are built into the formula, which can reduce specificity in elderly or very obese populations.

clinical pearls

  • NFS and FIB-4 are both first-line non-invasive fibrosis tests for NAFLD. FIB-4 is simpler (4 variables vs 6) and often used as the initial screen, with NFS or elastography as second-line for indeterminate FIB-4 results.
  • The formula is: −1.675 + (0.037 × age) + (0.094 × BMI) + (1.13 × IFG/diabetes [1=yes, 0=no]) + (0.99 × AST/ALT ratio) − (0.013 × platelets) − (0.66 × albumin g/dL).
  • The 'NAFLD' in the name is being replaced by 'MASLD' (metabolic dysfunction-associated steatotic liver disease) per the 2023 Delphi consensus. The score remains valid under the new nomenclature.
  • Like FIB-4, the NFS is better at ruling OUT advanced fibrosis (high NPV) than ruling it IN. A high NFS still requires confirmation with elastography or biopsy.
  • Both FIB-4 and NFS lose specificity in patients >65 due to age being a component of both formulas. In elderly patients, consider going directly to transient elastography.

related tools

fib-4Simpler first-line fibrosis screeningchild-pughIf cirrhosis already establishedmeldIf advanced liver disease