NAFLD Fibrosis Score Calculator
Calculate the NFS to predict advanced fibrosis in non-alcoholic fatty liver disease patients.
NFS Interpretation Guide
| NFS Score | Fibrosis Stage | Clinical Significance |
|---|---|---|
| <-1.455 | F0-F2 | Excludes advanced fibrosis (NPV 93%, sensitivity 90%) |
| -1.455 to 0.676 | Indeterminate | Further evaluation recommended (elastography or biopsy) |
| >0.676 | F3-F4 | Advanced fibrosis likely (PPV 82%, specificity 98%) |
NAFLD Fibrosis Score Formula
NFS = -1.675 + 0.037 × age + 0.094 × BMI + 1.13 × IFG/diabetes + 0.99 × (AST/ALT) - 0.013 × platelets - 0.66 × albumin
Where:
- Age is in years
- BMI is in kg/m²
- IFG/diabetes: 1 if present, 0 if absent
- AST and ALT in U/L
- Platelet count in ×10⁹/L
- Albumin in g/dL
Clinical Information
What is the NAFLD Fibrosis Score?
The NAFLD Fibrosis Score (NFS) is a validated non-invasive scoring system specifically developed to identify advanced fibrosis (stages F3-F4) in patients with non-alcoholic fatty liver disease (NAFLD). It combines readily available clinical and laboratory parameters to predict the likelihood of advanced liver scarring without the need for liver biopsy.
When to Use NFS
- Initial risk stratification in newly diagnosed NAFLD patients
- Monitoring disease progression in established NAFLD/NASH
- Determining need for hepatology referral
- Deciding whether liver biopsy is necessary
- Assessing response to lifestyle interventions or pharmacotherapy
- Screening high-risk populations (type 2 diabetes, metabolic syndrome)
Performance Characteristics
- AUROC for advanced fibrosis: 0.84-0.88
- Low cutoff (<-1.455): NPV 93%, Sensitivity 90%
- High cutoff (>0.676): PPV 82%, Specificity 98%
- Approximately 25-30% of patients fall into indeterminate zone
- Validated in multiple international cohorts
Advantages
- Specifically developed and validated for NAFLD population
- Uses readily available clinical and laboratory data
- High negative predictive value for excluding advanced fibrosis
- Cost-effective screening tool
- Can be repeated frequently for longitudinal monitoring
- Endorsed by major hepatology societies (AASLD, EASL)
Limitations
- Large indeterminate zone requiring additional testing
- Less accurate in younger patients (<35 years)
- May be affected by conditions altering component variables
- Cannot distinguish between intermediate fibrosis stages
- Not validated in patients with other liver diseases
- BMI may underestimate adiposity in sarcopenic patients
Clinical Management by Score
NFS <-1.455 (Low Risk):
- Advanced fibrosis unlikely, liver biopsy not routinely needed
- Focus on lifestyle modifications (diet, exercise, weight loss)
- Treat metabolic comorbidities (diabetes, dyslipidemia, hypertension)
- Reassess NFS annually or with significant clinical change
- Primary care management usually appropriate
NFS -1.455 to 0.676 (Indeterminate):
- Cannot rule in or exclude advanced fibrosis
- Consider additional non-invasive testing (FibroScan, FIB-4, ELF)
- Hepatology referral for further evaluation
- May need liver biopsy if other tests inconclusive
- Initiate intensive lifestyle intervention
- Consider pharmacotherapy if NASH confirmed
NFS >0.676 (High Risk):
- High probability of advanced fibrosis or cirrhosis
- Urgent hepatology referral indicated
- Screen for varices (esophagogastroduodenoscopy if cirrhosis)
- Hepatocellular carcinoma surveillance (ultrasound every 6 months)
- Assess for liver transplant candidacy if decompensated
- Aggressive treatment of metabolic risk factors
- Consider enrollment in clinical trials for NASH therapies
Frequently Asked Questions
What does a high NAFLD Fibrosis Score mean?
A score greater than 0.676 indicates high probability (82% positive predictive value) of advanced liver fibrosis (F3-F4). This suggests significant liver damage and scarring, increasing risk of progression to cirrhosis and its complications. Patients with high scores require hepatology referral, surveillance for complications, and aggressive treatment of underlying metabolic conditions.
Can I use NFS if I have other liver conditions besides NAFLD?
The NFS was specifically developed and validated for NAFLD patients and should not be used in patients with other primary liver diseases (viral hepatitis, alcohol-related liver disease, autoimmune hepatitis, etc.). For those conditions, other fibrosis scoring systems like FIB-4 or APRI may be more appropriate. Always ensure NAFLD is the primary liver disease before using NFS.
What should I do if my score is in the indeterminate range?
An indeterminate NFS (-1.455 to 0.676) affects about 25-30% of NAFLD patients and indicates uncertainty about fibrosis stage. Next steps typically include additional non-invasive testing such as vibration-controlled transient elastography (FibroScan), Enhanced Liver Fibrosis (ELF) test, or consideration of liver biopsy. Consultation with a hepatologist is recommended to determine the best approach for your specific situation.
How can I improve my NAFLD Fibrosis Score?
While age cannot be modified, other components can improve with lifestyle changes. Weight loss of 7-10% body weight can improve liver inflammation and potentially reduce fibrosis. This involves dietary modifications, regular exercise, and sometimes medications for diabetes or weight management. Improved metabolic control can favorably impact AST/ALT ratio, platelet count, and albumin levels, potentially lowering your score over time.
How often should NFS be calculated?
For patients with low-risk scores, annual reassessment is typically sufficient unless there are significant clinical changes. During active weight loss interventions or pharmacologic treatment, more frequent monitoring (every 6-12 months) may be helpful to track response. High-risk patients should have ongoing hepatology follow-up with surveillance protocols that may include more frequent comprehensive assessments.
Does diabetes affect my NFS interpretation?
Yes, diabetes or impaired fasting glucose is included in the NFS formula and significantly increases the score (adds 1.13 points). Diabetes is both a risk factor for NAFLD progression and a component of the scoring system. Good glycemic control is essential for NAFLD management, though it won't change your NFS calculation unless you've been misclassified as diabetic.
Can NFS distinguish between simple steatosis and NASH?
No, NFS is designed to assess fibrosis stage, not to distinguish between simple steatosis (fat accumulation alone) and NASH (fat plus inflammation). Both conditions can have varying degrees of fibrosis. Liver biopsy remains the gold standard for definitively diagnosing NASH. However, higher NFS scores suggest more advanced disease and higher likelihood of NASH with significant fibrosis.
Should I combine NFS with other fibrosis markers?
Yes, combining NFS with other non-invasive markers can improve diagnostic accuracy. Many experts recommend calculating both NFS and FIB-4, as they use different variables. When both are low, advanced fibrosis is very unlikely. When both are high, advanced fibrosis is very likely. Discordant results or indeterminate scores on both tests typically warrant additional evaluation with elastography or other advanced testing.