FIB-4 Score Calculator — Non-Invasive Liver Fibrosis Index
The FIB-4 (Fibrosis-4) score is a validated non-invasive index that combines routine laboratory values (age, AST, ALT, and platelet count) to estimate the probability of advanced liver fibrosis in patients with chronic liver disease.
About
The FIB-4 score was developed and validated by Sterling et al. in 2006 as a simple, non-invasive index to predict advanced liver fibrosis in patients with chronic liver disease. It uses four readily available clinical variables: age, aspartate aminotransferase (AST), alanine aminotransferase (ALT), and platelet count. The FIB-4 index has been validated across multiple etiologies of liver disease including NAFLD, hepatitis B, hepatitis C, and alcoholic liver disease. The score stratifies patients into low probability (F0-F1), indeterminate, and high probability (F3-F4) of advanced fibrosis. Age-adjusted cutoffs are recommended for patients aged 65 years and older, as the original cutoffs are less specific in older populations. FIB-4 is widely endorsed by international guidelines including AASLD, EASL, and AGA as a first-line screening tool for advanced fibrosis, reducing the need for invasive liver biopsy.
Formula
FIB-4 = (Age × AST) / (Platelets × √ALT)
FIB-4 is calculated using four parameters: Age (in years), AST (aspartate aminotransferase in U/L), ALT (alanine aminotransferase in U/L), and Platelet count (×10⁹/L). The square root of ALT is calculated first, then multiplied by the platelet count to form the denominator. The numerator is age multiplied by AST. The resulting score typically ranges from 0 to 10+, with higher scores indicating a greater probability of advanced fibrosis. For patients under 65 years: FIB-4 <1.45 excludes advanced fibrosis (NPV >90%), 1.45-3.25 is indeterminate requiring further testing, >3.25 suggests advanced fibrosis (F3-F4). For patients aged 65 and older, the low-risk cutoff is raised to <2.0 to maintain specificity, as the standard cutoff tends to overestimate fibrosis risk in older populations. FIB-4 should not be used in isolation for clinical decision-making; results in the indeterminate range require confirmation with elastography or other non-invasive tests.
Score Interpretation
The FIB-4 score is one of the most widely validated non-invasive markers for liver fibrosis, endorsed by major hepatology guidelines (AASLD, EASL, AGA) as a first-line screening tool. Its clinical relevance stems from the use of readily available, low-cost laboratory tests that are routinely ordered in patients with liver disease, eliminating the need for specialized equipment. FIB-4 performs well across multiple liver disease etiologies including NAFLD (AUROC 0.80-0.86 for advanced fibrosis), hepatitis C, hepatitis B, and alcoholic liver disease. A key strength is the high negative predictive value (NPV >90%) of a low FIB-4 score, which reliably excludes advanced fibrosis and avoids unnecessary referrals. The main limitation is the large indeterminate range (1.45-3.25) which requires further testing in approximately 30-40% of patients. The age-adjusted cutoff for patients ≥65 years improves specificity in older populations where the standard cutoff tends to overestimate fibrosis risk.
Low probability (F0-F1) — Age <65 — 0–1.44
FIB-4 <1.45. Low probability of advanced fibrosis. No further fibrosis evaluation needed. Reassess in 1-2 years.
Management: Continue routine monitoring of liver enzymes. Reassess FIB-4 in 1-2 years.
Indeterminate — further evaluation needed — 1.45–3.25
FIB-4 1.45-3.25. Indeterminate probability of advanced fibrosis. Further evaluation with elastography is recommended.
Management: Perform transient elastography (FibroScan) or MRE. Consider liver biopsy if non-invasive tests are discordant. Reassess FIB-4 every 6-12 months.
High probability (F3-F4) — advanced fibrosis — 3.26+
FIB-4 >3.25. High probability of advanced fibrosis (F3-F4). Refer to hepatology for further management.
Management: Refer to hepatology. Perform transient elastography for confirmation. Screen for varices and HCC. Start HCC surveillance.
Reference Ranges
| Population | Normal Range | Notes |
|---|---|---|
| Adults <65 years with chronic liver disease | <1.45 (Low) — Excludes advanced fibrosis (F0-F1) | NPV >90% for excluding advanced fibrosis |
Dr. Mahmoud El-Sayed
Dr. Mahmoud is an endocrinology consultant with expertise in metabolic liver disease assessment.
View medical review board & editorial policy →Example Calculation
A 52-year-old patient with NAFLD undergoes routine liver fibrosis assessment. Labs: AST 45 U/L, ALT 68 U/L, Platelets 220 ×10⁹/L. FIB-4 = (52 × 45) / (220 × √68) = 2340 / (220 × 8.25) = 2340 / 1815 = 1.29. Since the patient is under 65 and the score is <1.45, this indicates a low probability of advanced fibrosis (F0-F1). No further fibrosis evaluation is required, with reassessment recommended in 1-2 years.
Related Conditions
Related Medications
Common Mistakes
Using standard FIB-4 cutoffs for patients aged 65 and older
For patients ≥65 years, use the age-adjusted cutoff of <2.0 for low probability of advanced fibrosis. The standard cutoff of <1.45 tends to overestimate fibrosis risk in older populations due to age-related physiological changes in liver enzymes and platelet counts.
Using FIB-4 in patients with acute hepatitis or acute liver injury
FIB-4 is validated for chronic liver disease, not acute liver injury. Acute elevations in AST/ALT can falsely elevate the FIB-4 score. Wait until liver enzymes have stabilised (typically 3-6 months after acute episode) before performing FIB-4 assessment.
Frequently Asked Questions
What does a low FIB-4 score mean?
Why is there an age-adjusted cutoff for FIB-4?
How does FIB-4 compare to liver biopsy?
References
- Sterling RK, Lissen E, Clumeck N, et al. Development of a simple noninvasive index to predict significant fibrosis in patients with HIV/HCV coinfection. Hepatology. 2006;43(6):1317-1325. PubMed
- Shah AG, Lydecker A, Murray K, et al. Comparison of noninvasive markers of fibrosis in patients with nonalcoholic fatty liver disease. Clin Gastroenterol Hepatol. 2009;7(10):1104-1112. PubMed
- McPherson S, Hardy T, Dufour JF, et al. Age as a confounding factor for the accurate non-invasive diagnosis of advanced NAFLD fibrosis. Am J Gastroenterol. 2017;112(5):740-751. PubMed
- European Association for the Study of the Liver. EASL Clinical Practice Guidelines on non-invasive tests for evaluation of liver disease severity and prognosis — 2021 update. J Hepatol. 2021;75(3):659-689. PubMed