Calculate the FIB-4 index for liver fibrosis staging using age, AST, ALT, and platelets. Includes age-adjusted cutoffs, APRI comparison, METAVIR staging, and referral guidance.
The FIB-4 Index Calculator estimates the degree of liver fibrosis using four readily available laboratory values: patient age, AST (aspartate aminotransferase), ALT (alanine aminotransferase), and platelet count. Originally developed by Sterling et al. (2006) for HIV-HCV co-infected patients, FIB-4 has since been validated across virtually all chronic liver diseases including NAFLD/MASLD, hepatitis B, hepatitis C, and alcohol-related liver disease.
FIB-4 has become the recommended first-line non-invasive test for fibrosis screening in major guidelines including AASLD, EASL, and ACG. Its greatest clinical utility is its high negative predictive value (90–95%): a low FIB-4 score reliably excludes advanced fibrosis (F3–F4), reducing unnecessary specialist referrals and invasive procedures. Patients in the indeterminate range are triaged to liver stiffness measurement (transient elastography / FibroScan) for further risk stratification.
The calculator implements age-adjusted cutoffs per AASLD 2023 recommendations: lower cutoffs for patients under 35 (improved sensitivity) and adjusted thresholds for patients over 65 (improved specificity). It also computes APRI for comparison and provides the complete METAVIR fibrosis staging framework with management recommendations at each step.
FIB-4 uses routine blood tests available in any clinical setting, requires no specialized equipment, and has excellent performance for ruling out advanced fibrosis. With NAFLD/MASLD affecting 25–30% of the global adult population, efficient non-invasive screening is essential to identify the ~5–10% with advanced fibrosis who need specialist care. Keep these notes focused on your operational context.
FIB-4 = (Age [years] × AST [U/L]) / (Platelet count [×10⁹/L] × √ALT [U/L]) Standard cutoffs (age 35–65): • <1.30 = Low risk of advanced fibrosis (F3–F4) • 1.30–2.67 = Indeterminate • >2.67 = High risk of advanced fibrosis Age-adjusted (age <35): <0.70 low risk Age-adjusted (age ≥65): <2.00 low risk APRI = (AST / Upper Limit Normal) / Platelets × 100
Result: FIB-4 = 2.67 — Indeterminate range. Recommend liver stiffness measurement.
FIB-4 = (55 × 55) / (150 × √48) = 3025 / (150 × 6.93) = 3025 / 1039.5 = 2.91. This falls just above the 2.67 high-risk cutoff, suggesting significant risk of advanced fibrosis. The patient should be referred for liver stiffness measurement (FibroScan) and hepatology evaluation. If cirrhosis is confirmed, HCC surveillance and variceal screening are indicated.
The AASLD 2023 Practice Guidance recommends FIB-4 as the initial non-invasive test for fibrosis assessment in all patients with chronic liver disease. The recommended pathway: 1) Calculate FIB-4 using routine labs, 2) Low risk (<1.30 or age-adjusted) → reassess in 1–2 years, 3) Indeterminate (1.30–2.67) → proceed to liver stiffness measurement, 4) High risk (>2.67) → hepatology referral with or without confirmatory elastography. This algorithm reduces specialist referrals by 50–70% while maintaining >90% negative predictive value.
Fibrosis is not irreversible. Treatment of the underlying cause can lead to fibrosis regression: sustained virologic response (SVR) in hepatitis C reverses fibrosis in 50–70% of patients over 5 years; significant weight loss (≥7–10% body weight) improves NASH fibrosis by at least one stage in 45–65% of patients; alcohol cessation in compensated alcohol-related liver disease allows fibrosis improvement. Serial FIB-4 monitoring every 6–12 months can track improvement, though fibrosis regression takes years and FIB-4 changes may lag behind histological improvement.
FIB-4 should not be used in: acute hepatitis (falsely elevated), patients <18 years, pregnancy, or isolated thrombocytopenia from non-hepatic causes (ITP, bone marrow disorders). It performs best as a rule-out test (high NPV) and less well as a rule-in test (moderate PPV). No single non-invasive test is perfect — the combination of multiple modalities (FIB-4 + elastography) provides the most accurate assessment short of biopsy.
FIB-4 is a composite score that estimates the likelihood of advanced liver fibrosis (METAVIR F3–F4). It combines four variables that individually reflect liver injury and portal hypertension: age (fibrosis accumulates over time), AST (marker of hepatocyte damage), ALT (hepatocyte damage — the AST/ALT ratio increases with fibrosis), and platelet count (decreases with portal hypertension and decreased thrombopoietin production). FIB-4 does not directly measure fibrosis — it statistically estimates the probability based on surrogate markers.
For patients with low FIB-4 (<1.30): recheck every 1–2 years if the underlying liver disease persists (e.g., ongoing NAFLD, untreated hepatitis B). For the indeterminate zone: recheck after any intervention (weight loss, viral treatment, alcohol cessation) to see if the score improves below the low-risk cutoff. FIB-4 should not be recalculated during acute events (viral hepatitis flares, DILI) as transient transaminase elevations will give falsely elevated scores.
FIB-4 is a blood-test-based calculation (no equipment needed, available anywhere, free). FibroScan (transient elastography) is an ultrasound-based device that directly measures liver stiffness in kilopascals (kPa). FibroScan is more accurate but requires specialized equipment, trained operators, and costs more. The current recommended clinical pathway is: FIB-4 first (screening) → FibroScan for patients in the indeterminate zone (confirmation). This sequential approach reduces unnecessary FibroScan referrals by ~50%.
Yes — FIB-4 has been extensively validated in NAFLD/MASLD populations and is recommended as the first-line screening test by AASLD, EASL, and ACG guidelines. In NAFLD, FIB-4 <1.30 has a NPV of ~90% for excluding advanced fibrosis. The main limitation is the large indeterminate zone (~30–40% of NAFLD patients fall between 1.30–2.67), which is why the sequential approach with FibroScan or ELF test is recommended. The NAFLD Fibrosis Score (NFS) is an alternative that incorporates BMI, diabetes status, and albumin.
No — FIB-4 was designed and validated specifically for detecting advanced fibrosis (F3–F4). It has poor sensitivity and specificity for distinguishing F0-F1 from F2. This is a known limitation of all non-invasive fibrosis tests (including elastography to some degree). For early fibrosis detection, liver biopsy remains the gold standard. However, from a clinical management perspective, the most important distinction is between F0-F2 (favorable prognosis) and F3-F4 (significantly increased morbidity/mortality), which FIB-4 addresses well.
Age is a component of the FIB-4 formula (numerator), so older patients inherently get higher scores regardless of fibrosis status. Using the standard <1.30 cutoff in patients ≥65 leads to excessive false positives (~50–60% of elderly patients without fibrosis score >1.30). The AASLD 2023 guidelines recommend a <2.0 low-risk cutoff for age ≥65. Conversely, young patients (<35) may have falsely reassuring low FIB-4 values; a lower cutoff of 0.70 improves sensitivity in this age group.