FIB-4 Index Calculator
Assess liver fibrosis risk non-invasively using age and routine blood tests. The FIB-4 index is recommended by NICE NG49 for initial assessment in non-alcoholic fatty liver disease (NAFLD).
FIB-4 Calculator
FIB-4 Formula
Where age is in years, AST and ALT are in U/L, and platelets are in 109/L.
About the FIB-4 Index
The FIB-4 index is a non-invasive marker of liver fibrosis that uses readily available clinical and laboratory data. It was originally developed for HIV/HCV coinfected patients but is now widely used for NAFLD assessment.
Why Use FIB-4?
- Non-invasive - avoids need for liver biopsy in many cases
- Simple - uses routine blood tests
- Validated - extensively studied in NAFLD and viral hepatitis
- Recommended - by NICE, EASL, and other guidelines
- Cost-effective - no additional testing required
Clinical Application:
FIB-4 is used as a first-line test to identify patients who need further assessment (e.g., transient elastography/FibroScan) versus those at low risk who can be managed in primary care.
FIB-4 Score Interpretation
| FIB-4 Score | Risk Category | Fibrosis Likelihood | Recommended Action |
|---|---|---|---|
| < 1.30 | Low risk | Advanced fibrosis (F3-F4) excluded with ~90% NPV |
|
| 1.30 - 2.67 | Indeterminate | Further assessment needed |
|
| > 2.67 | High risk | ~65% PPV for advanced fibrosis |
|
NICE recommends using FIB-4 (or ELF test) as the initial assessment for advanced fibrosis in adults with NAFLD. Patients with indeterminate or high scores should be referred for specialist assessment, which may include transient elastography.
Age-Adjusted Considerations
Patients ≥ 65 Years
The standard cut-offs may be less accurate in older patients because:
- Age is in the numerator of the formula
- Platelet counts may naturally decrease with age
- Higher false positive rate in elderly patients
Suggested adjustment for age ≥ 65:
- Consider using < 2.0 as low risk cut-off
- Or use alternative scoring (ELF test)
- Clinical judgement essential
Patients < 35 Years
In younger patients:
- Age factor means lower scores overall
- May miss fibrosis in young patients with rapidly progressive disease
- Standard cut-offs generally apply
Clinical note: While advanced fibrosis is less common in young patients, the FIB-4 validation is primarily in patients aged 35-65. Consider lower threshold for investigation if clinical suspicion is high.
When to Use FIB-4
Appropriate Use
- NAFLD/MAFLD - initial fibrosis assessment
- Chronic hepatitis B or C - before/after treatment
- Alcohol-related liver disease - fibrosis staging
- Primary care screening - identifying who needs referral
- Serial monitoring - tracking fibrosis progression
Limitations / Cautions
- Acute liver injury - transaminases fluctuate
- Known cirrhosis - already confirmed, use for monitoring only
- Other causes of thrombocytopenia - ITP, medications, etc.
- Haematological conditions - affecting platelet count
- Age extremes - less validated <35 or >65 years
- HIV coinfection - may need different cut-offs
Frequently Asked Questions
| FIB-4 | FibroScan (TE) |
|---|---|
| Blood-based calculation | Ultrasound-based liver stiffness measurement |
| Free (uses routine tests) | Requires specialist equipment |
| First-line screening test | Second-line confirmatory test |
| Good for ruling out fibrosis | Better for confirming/staging fibrosis |
| ~30% indeterminate results | More definitive results |
In practice, FIB-4 is used first, and FibroScan is used for patients with indeterminate or high FIB-4 scores.
NICE recommends:
- Low risk (FIB-4 < 1.30): Recheck every 3 years
- Risk factors present: Consider more frequent monitoring
- After intervention: Recheck to assess response (e.g., after weight loss, alcohol cessation)
More frequent monitoring may be appropriate if risk factors worsen (weight gain, diabetes development, increased alcohol use).
Yes, but with some caveats:
- FIB-4 was validated primarily in NAFLD and viral hepatitis
- In alcohol-related liver disease, AST is often disproportionately elevated (AST:ALT ratio >2)
- This may artificially increase the FIB-4 score
- Recent heavy alcohol use can cause acute transaminitis, affecting accuracy
Consider retesting after a period of abstinence if acute alcohol effect is suspected.
Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease, affecting ~25% of the global population. The spectrum includes:
- Simple steatosis - fat accumulation without inflammation (benign)
- NASH - steatosis with inflammation and hepatocyte injury
- Fibrosis - scarring due to chronic injury
- Cirrhosis - advanced fibrosis with architectural distortion
Fibrosis stage is the strongest predictor of liver-related outcomes and mortality. Identifying patients with significant fibrosis (F2+) or advanced fibrosis (F3-F4) allows targeted intervention and monitoring.
Several non-invasive fibrosis markers are available:
- NAFLD Fibrosis Score (NFS) - uses age, BMI, diabetes, transaminases, platelets, albumin
- ELF (Enhanced Liver Fibrosis) test - blood test measuring HA, PIIINP, TIMP-1
- APRI (AST to Platelet Ratio Index) - simpler formula, less accurate
- Hepascore, FibroTest/FibroSure - proprietary blood panels
- Transient Elastography (FibroScan) - ultrasound-based stiffness measurement
- MR Elastography - MRI-based, most accurate non-invasive method
FIB-4 and NFS are commonly used first-line tests because they use readily available data.
Disclaimer
This calculator is provided for educational and informational purposes only. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment.
- Always seek the advice of a qualified healthcare provider with any questions regarding a medical condition.
- Never disregard professional medical advice or delay seeking it because of information from this tool.
- Clinical decision-making should always incorporate the full clinical context, patient preferences, and local protocols.
- The creators of this tool accept no liability for decisions made based on its output.
If you are a patient: please discuss any results with your healthcare provider. This tool is designed for use by medical professionals and may not be appropriate for self-assessment.
References
- Sterling RK, et al. (2006). Development of a simple noninvasive index to predict significant fibrosis in patients with HIV/HCV coinfection. Hepatology, 43(6), 1317-1325.
- NICE (2016). Non-alcoholic fatty liver disease (NAFLD): assessment and management (NG49).
- McPherson S, et al. (2017). Simple non-invasive fibrosis scoring systems can reliably exclude advanced fibrosis in patients with non-alcoholic fatty liver disease. Gut, 66(7), 1321-1328.
- Shah AG, et al. (2009). Comparison of noninvasive markers of fibrosis in patients with nonalcoholic fatty liver disease. Clinical Gastroenterology and Hepatology, 7(10), 1104-1112.
- European Association for the Study of the Liver. (2021). EASL Clinical Practice Guidelines on non-invasive tests for evaluation of liver disease severity and prognosis. Journal of Hepatology, 75(3), 659-689.