FIB-4 Index Calculator
Calculate your Fibrosis-4 (FIB-4) index to assess the statistical likelihood of advanced liver fibrosis using standard clinical blood markers and age.
FIB-4 Risk Categories
What Is a FIB-4 Index Calculator?
A FIB-4 Index Calculator is a non-invasive hepatic biomarker reference tool designed to evaluate ratios and indices of liver health. By analyzing routine biochemical panel inputs such as AST, ALT, platelets, or bilirubin, it calculates validated clinical scores (such as the De Ritis ratio or FIB-4 index) to provide educational insight into liver health and warrant follow-up consultation with a physician.
How to Use This Calculator
- Input your age in years.
- Input your AST and ALT levels in U/L.
- Input your Platelet Count (in $10^9/\text{L}$ or $10^3/\mu\text{L}$, e.g., 250).
- Click 'Calculate FIB-4' to review your fibrosis risk category.
How This Calculator Works
Derived by Sterling et al.: $\text{FIB-4} = \frac{\text{Age (years)} \times \text{AST (U/L)}}{\text{Platelets } (10^9/\text{L}) \times \sqrt{\text{ALT (U/L)}}}$. It combines transaminase inflammation with thrombocytopenia (low platelets caused by portal hypertension and splenic sequestration).
Understanding Your Results
In NAFLD: A score <1.30 (<2.0 in adults aged ≥65) has a >90% negative predictive value, ruling out advanced fibrosis. A score >2.67 indicates a high probability of advanced fibrosis (F3-F4), warranting liver elastography (FibroScan) or hepatology referral. Scores between 1.30 and 2.67 represent an indeterminate zone.
Frequently Asked Questions
What is the primary clinical purpose of FIB-4?
FIB-4 serves as a validated frontline triage tool recommended by the American Association for the Study of Liver Diseases (AASLD) to identify which patients with fatty liver require specialist evaluation.
Can FIB-4 replace a liver biopsy?
FIB-4 reliably rules out advanced fibrosis in low-risk individuals, reducing the need for invasive liver biopsies. In intermediate or high scores, secondary testing with transient elastography (FibroScan) is recommended.
Why do low platelets increase the FIB-4 score?
As liver fibrosis progresses to cirrhosis, portal hypertension develops, causing the spleen to enlarge (splenomegaly) and trap platelets, making declining platelet counts an important biological indicator of progressive fibrosis.
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Important Limitations & Medical Disclaimer
Notice: The FIB-4 index provides statistical risk stratification and is NOT a definitive diagnosis of cirrhosis. Clinical decisions require comprehensive hepatology evaluation and vibration-controlled transient elastography (VCTE).