FIB-4 Calculator: Liver Fibrosis Assessment
Calculate the FIB-4 score to non-invasively assess liver fibrosis stage using age, AST, ALT, and platelet count.
Enter age, AST, ALT, and platelet count from standard blood tests to compute FIB-4 and screen for advanced liver fibrosis without a biopsy.
FIB-4 Calculator: Liver Fibrosis Assessment
Calculate the FIB-4 score to non-invasively assess liver fibrosis stage using age, AST, ALT, and platelet count.
About the FIB-4 Calculator
The Fibrosis-4 (FIB-4) index is a simple, non-invasive scoring system developed to estimate the stage of liver fibrosis in patients with chronic liver disease, without the need for a liver biopsy. It was originally developed and validated in patients co-infected with HIV and hepatitis C virus, and has since been extensively validated in hepatitis B, non-alcoholic fatty liver disease (NAFLD), and other chronic liver conditions. The FIB-4 score is calculated from four readily available variables: the patient's age in years, aspartate aminotransferase (AST) in U/L, alanine aminotransferase (ALT) in U/L, and platelet count in ×10⁹/L. The formula is: FIB-4 = (Age × AST) ÷ (Platelet count × √ALT).
The biological rationale behind these variables reflects their relationships to liver injury and function. AST is released from damaged hepatocytes and rises with active liver inflammation and injury. ALT is a more liver-specific enzyme that also rises with hepatocellular damage. Platelet count decreases as fibrosis progresses, because a fibrotic liver impairs portal blood flow, leading to splenomegaly and platelet sequestration (hypersplenism), and also because the fibrotic liver produces less thrombopoietin. Age is included because fibrosis tends to progress with time and older patients at the same histological stage have worse outcomes. The formula combines these trends in a way that has proven clinically useful across large validation cohorts.
The standard thresholds divide patients into three risk categories. A FIB-4 score below 1.30 indicates a low probability of advanced fibrosis (Metavir stages F0–F1), with a negative predictive value of approximately 90% in most validation studies — meaning most patients in this category do not have significant fibrosis. A score above 2.67 indicates a high probability of advanced fibrosis (F3–F4, including cirrhosis), with a positive predictive value of approximately 65–80% depending on the population. The intermediate zone between 1.30 and 2.67 is indeterminate and typically warrants further evaluation with elastography (FibroScan), other non-invasive fibrosis markers such as APRI or the Enhanced Liver Fibrosis (ELF) panel, or in some cases liver biopsy.
The FIB-4 index has gained particular prominence in the screening and monitoring of non-alcoholic fatty liver disease / non-alcoholic steatohepatitis (NAFLD/NASH), where it is recommended by major liver societies including the AASLD and EASL as an initial risk stratification tool in primary care and general medicine. A low FIB-4 score in a patient with NAFLD provides reassurance and avoids the need for specialist referral in many cases. High scores prompt referral to hepatology for further evaluation and potential treatment.
Important limitations of FIB-4 include reduced accuracy in patients under 35 years old (where the formula tends to underestimate fibrosis), in patients with very elevated liver enzymes due to acute hepatitis (where AST and ALT rise disproportionately to fibrosis stage), and in conditions causing thrombocytopenia from causes other than liver fibrosis. The score should always be interpreted alongside the clinical context, imaging findings, and other laboratory tests. It is a screening tool, not a definitive diagnostic test.
FIB-4 score examples
Click any example to load typical values into the calculator.
| Age / AST / ALT / Platelets | FIB-4 Score | Risk Category |
|---|---|---|
| Age 35 / AST 25 / ALT 30 / Platelets 250 | 0.64 | Low risk — FIB-4 <1.30 indicates minimal fibrosis (F0–F1); routine monitoring appropriate. |
| Age 55 / AST 60 / ALT 45 / Platelets 120 | 4.10 | High risk — FIB-4 >2.67 suggests advanced fibrosis (F3–F4); hepatology referral recommended. |
| Age 48 / AST 40 / ALT 35 / Platelets 160 | 2.03 | Intermediate — FIB-4 1.30–2.67; further evaluation with elastography or ELF panel advised. |
| Age 65 / AST 90 / ALT 40 / Platelets 80 | 11.56 | Very high risk — strongly suggests cirrhosis; urgent hepatology evaluation needed. |
How to use the FIB-4 Calculator
- Obtain a standard liver function panel (LFTs) and complete blood count (CBC) from recent blood tests.
- Enter the patient's age in years, AST level in U/L, and ALT level in U/L.
- Enter the platelet count in ×10⁹/L (also called 10³/µL or thousands/µL on most reports).
- Click Calculate FIB-4 Score to compute the index and see the fibrosis risk category.
- Interpret: FIB-4 <1.30 = low risk; 1.30–2.67 = intermediate (needs further testing); >2.67 = high risk, refer to hepatology.
FIB-4 calculator FAQ
What is the FIB-4 index used for?
FIB-4 is used to estimate the degree of liver fibrosis non-invasively in patients with chronic liver disease — including hepatitis B, hepatitis C, and NAFLD/NASH. It helps clinicians triage patients, determine who needs specialist referral, and monitor disease progression over time without repeated biopsies.
What does a FIB-4 score above 2.67 mean?
A score above 2.67 indicates a high probability of advanced liver fibrosis (F3–F4 or cirrhosis). While not diagnostic on its own, it warrants hepatology referral for further investigation, typically including liver elastography (FibroScan) and possibly liver biopsy to confirm the fibrosis stage.
Is FIB-4 accurate in all age groups?
FIB-4 is less reliable in patients younger than 35, where it tends to underestimate fibrosis, and may be less accurate in patients older than 65, where age alone drives the score upward. Many guidelines suggest adjusted thresholds (e.g., 1.30/2.67 for ages 35–65, 2.00/4.00 outside this range) to improve specificity in older patients.
How does FIB-4 compare to liver biopsy?
Liver biopsy is the gold standard for fibrosis staging but is invasive, costly, and carries a small risk of complications. FIB-4 is a practical non-invasive alternative for initial screening. A low FIB-4 reliably excludes advanced fibrosis in most patients, while a high score identifies those who most benefit from biopsy or elastography.
Can I use FIB-4 to monitor treatment response?
Yes. Serial FIB-4 measurements over months or years can track disease progression or regression. Successful antiviral treatment for hepatitis B or C typically reduces AST and ALT and may improve platelet counts, all of which lower the FIB-4 score. However, large decreases in score can also reflect reduced inflammation rather than actual fibrosis reversal.
Is this calculator a substitute for medical advice?
No. FIB-4 is a screening tool for educational and clinical reference use. The result should be interpreted by a qualified physician alongside the patient's full medical history, physical examination, imaging, and other laboratory findings. Do not make treatment decisions based solely on this calculator.