FIB-4 Index
Calculate the FIB-4 index for liver fibrosis risk assessment using age, AST, ALT, and platelet count. Free online NAFLD fibrosis scoring tool with interpretation and charts.
About This Calculator
The FIB-4 (Fibrosis-4) Index Calculator is a non-invasive clinical tool designed to assess the probability of advanced liver fibrosis in patients with chronic liver disease. By combining four routinely measured parameters — age, AST (aspartate aminotransferase), ALT (alanine aminotransferase), and platelet count — this calculator provides a validated estimate of fibrosis severity without requiring invasive procedures like liver biopsy. It is widely used by hepatologists, gastroenterologists, and primary care physicians for screening patients with NAFLD, hepatitis B, hepatitis C, and HIV-HCV co-infection.
The FIB-4 score is calculated using the formula: FIB-4 = (Age × AST) / (Platelet Count × √ALT). A score below 1.45 effectively rules out advanced fibrosis in approximately 95% of patients, while a score above 3.25 confirms advanced fibrosis in about 82% of cases. Scores between 1.45 and 3.25 are considered indeterminate and require further evaluation through elastography (FibroScan), MRI, or liver biopsy. The test performs best in adults aged 35–65 years and may produce false positives in older adults due to age-related physiological changes.
Regional Notes
India: NAFLD affects approximately 25–30% of the Indian population, making FIB-4 screening increasingly important. Liver function tests (LFT) and CBC are widely available at affordable rates (₹300–800) across major diagnostic labs. The FibroScan cost ranges from ₹3,000–8,000 and may be recommended for indeterminate FIB-4 results.
US: NAFLD affects about 25% of American adults. FIB-4 is recommended by the American Association for the Study of Liver Diseases (AASLD) as a first-line non-invasive test for fibrosis risk stratification. Medicare and most insurance plans cover LFT and CBC annually. Confirmatory FibroScan costs approximately $200–500 out-of-pocket.
UK: NICE guidelines recommend the FIB-4 index as the initial test for NAFLD-related fibrosis in primary care. The NHS offers LFT and CBC as part of routine health checks. Referral to secondary care (hepatology) is advised for indeterminate or high-risk scores. The Enhanced Liver Fibrosis (ELF) test is used as a second-line test.
Frequently Asked Questions
What is the FIB-4 index and what does it measure?
The FIB-4 (Fibrosis-4) index is a non-invasive scoring system that uses four parameters — age, AST, ALT, and platelet count — to estimate the probability of advanced liver fibrosis in patients with chronic liver disease including NAFLD, HCV, and HBV. It helps rule in or rule out significant fibrosis without requiring a liver biopsy.
How is the FIB-4 score calculated?
The FIB-4 score is calculated using the formula: FIB-4 = (Age × AST) / (Platelet Count × √ALT). Age is in years, AST and ALT are in U/L, and platelet count is in ×10⁹/L. For example, a 55-year-old with AST 45 U/L, ALT 60 U/L, and platelets 200×10⁹/L yields a FIB-4 score of (55 × 45) / (200 × √60) ≈ 1.60.
How do I interpret my FIB-4 score?
A FIB-4 score below 1.45 suggests low probability of advanced fibrosis and can rule it out in about 95% of patients. Scores between 1.45 and 3.25 are indeterminate and warrant further investigation such as liver biopsy or elastography. A score above 3.25 indicates high probability of advanced fibrosis, confirmed in about 82% of cases.
Is the FIB-4 calculator accurate for all age groups?
The FIB-4 index is most accurate for adults aged 35 to 65. Patients younger than 35 may receive false-negative results, while those over 65 may get false-positive results due to age-related changes in liver enzymes and platelet counts. Always interpret results in the context of the patient's full clinical picture.
What conditions can the FIB-4 index help assess?
The FIB-4 index is primarily used for patients with Non-Alcoholic Fatty Liver Disease (NAFLD), chronic hepatitis C (HCV), hepatitis B (HBV), and HIV-HCV co-infections. It is a validated non-invasive tool for assessing the risk of advanced liver fibrosis and cirrhosis.
Can the FIB-4 calculator replace a liver biopsy?
No, the FIB-4 index cannot fully replace a liver biopsy. It is a screening tool that helps identify patients who need further evaluation. A high FIB-4 score suggests advanced fibrosis but requires confirmation through additional imaging (FibroScan, MRI elastography) or biopsy. Always consult a hepatologist or gastroenterologist for a definitive diagnosis.
What is the difference between FIB-4 and APRI score?
Both FIB-4 and APRI (AST-to-Platelet Ratio Index) are non-invasive fibrosis scores. FIB-4 includes age and both AST and ALT, making it more accurate for NAFLD patients. APRI uses only AST and platelet count and is commonly used for hepatitis C. FIB-4 has better diagnostic accuracy for advanced fibrosis in NAFLD patients.
What blood tests do I need for the FIB-4 calculator?
You need three routine blood test results: AST (aspartate aminotransferase) in U/L, ALT (alanine aminotransferase) in U/L, and a complete blood count (CBC) showing platelet count in ×10⁹/L or per microliter. These tests are part of standard liver function panels and are widely available.