NAFLD Fibrosis Score Calculator
Calculate the NAFLD Fibrosis Score using clinical and lab values to help assess the risk of advanced liver fibrosis.
What Is the NAFLD Fibrosis Score?
The NAFLD Fibrosis Score is a validated, non-invasive clinical tool used to estimate the likelihood of advanced liver fibrosis in patients with non-alcoholic fatty liver disease (NAFLD). It combines routine laboratory values and demographic data to calculate a score that helps clinicians stratify patients by fibrosis risk, reducing the need for liver biopsy in many cases.
The score is derived from six variables: age, body mass index (BMI), presence of impaired fasting glucose or diabetes, platelet count, serum albumin, and the AST/ALT ratio. The resulting score categorizes patients into low, intermediate, or high probability of advanced fibrosis (stage F3–F4).
How the Score Is Calculated
The NAFLD Fibrosis Score uses the following formula:
Score = −1.675 + (0.037 × age in years) + (0.094 × BMI in kg/m²) + (1.13 × impaired fasting glucose or diabetes [yes = 1, no = 0]) + (0.99 × AST/ALT ratio) − (0.013 × platelet count in ×10⁹/L) − (0.66 × albumin in g/dL)
Each variable contributes independently to the final score. The formula was derived from a large cohort of NAFLD patients and validated in multiple independent populations.
Variable Definitions
- Age: Patient age in years at the time of assessment.
- BMI: Body mass index calculated as weight in kilograms divided by height in meters squared.
- Impaired fasting glucose or diabetes: Coded as 1 if the patient has a fasting glucose ≥ 110 mg/dL or a confirmed diagnosis of type 2 diabetes. Otherwise coded as 0.
- AST/ALT ratio: The ratio of aspartate aminotransferase to alanine aminotransferase, both measured in U/L.
- Platelet count: Measured in ×10⁹/L (or 10³/µL).
- Albumin: Serum albumin measured in g/dL.
Interpreting the Results
The calculated score is interpreted using established cut-off values:
| Score Range | Interpretation | Likelihood of Advanced Fibrosis (F3–F4) |
|---|---|---|
| < −1.455 | Low probability | Low (high negative predictive value) |
| −1.455 to 0.675 | Indeterminate | Uncertain; further evaluation recommended |
| > 0.675 | High probability | High (high positive predictive value) |
A score below −1.455 reliably rules out advanced fibrosis in most patients. A score above 0.675 strongly suggests the presence of advanced fibrosis. Patients in the indeterminate range require additional assessment, such as elastography or liver biopsy, to clarify fibrosis stage.
Practical Use Cases
- Primary care screening: Identify NAFLD patients who may need specialist referral for advanced fibrosis evaluation.
- Hepatology clinics: Reduce unnecessary liver biopsies by using the score as a first-line risk stratification tool.
- Longitudinal monitoring: Track score changes over time to assess disease progression or response to lifestyle interventions.
- Research settings: Stratify patient cohorts in clinical studies investigating NAFLD treatments or natural history.
Limitations and Considerations
- The score was validated in NAFLD patients and may not perform reliably in other liver disease etiologies.
- Approximately 25–30% of patients fall into the indeterminate range, requiring additional testing.
- The score has lower accuracy in patients with extreme BMI values or significant alcohol consumption history.
- Laboratory values must be measured within a reasonable timeframe for the score to be clinically valid.
- The score does not replace clinical judgment; it should be used as part of a comprehensive assessment.
Frequently Asked Questions
What is the difference between NAFLD and NASH?
NAFLD (non-alcoholic fatty liver disease) refers to the presence of fat in the liver without significant inflammation or liver damage. NASH (non-alcoholic steatohepatitis) is a more advanced form of NAFLD that includes inflammation and liver cell injury, which can progress to fibrosis and cirrhosis. The NAFLD Fibrosis Score is designed to detect advanced fibrosis, not to distinguish between NAFLD and NASH.
Can the NAFLD Fibrosis Score be used in patients without diabetes?
Yes. The score includes impaired fasting glucose or diabetes as one of six variables, but it can be calculated in patients without either condition. In such cases, the diabetes variable is set to 0, and the score still provides useful risk stratification based on the remaining variables.
How often should the NAFLD Fibrosis Score be recalculated?
There is no universal consensus, but many clinicians recalculate the score annually or when there is a significant change in clinical status, such as weight loss, development of diabetes, or changes in liver enzymes. Serial measurements can help track disease progression or response to treatment.
What should I do if the result is in the indeterminate range?
An indeterminate result means the score cannot reliably rule in or rule out advanced fibrosis. Additional evaluation is recommended, which may include liver stiffness measurement (elastography), enhanced liver fibrosis (ELF) test, or liver biopsy depending on clinical context and local resources.
Is the NAFLD Fibrosis Score accurate in elderly patients?
The score includes age as a variable, so it adjusts for age-related changes. However, extreme age values may affect performance. The original validation studies included patients across a broad age range, but clinicians should interpret results cautiously in very elderly patients, where age-related physiological changes may influence the score independently of liver fibrosis.