FIB-4 Liver Fibrosis Calculator

About the FIB-4 Liver Fibrosis Calculator

The FIB-4 index estimates the risk of advanced liver scarring (fibrosis) from four values almost every check-up has: age, the liver enzymes AST and ALT, and the platelet count. It is the first step guidelines recommend for people with fatty liver disease or metabolic risk factors: a low score makes advanced fibrosis unlikely, and a higher one calls for a second test such as elastography.

This calculator gives the FIB-4 with the working, places it in the risk bands of the AASLD practice guidance — below 1.3 low, 1.3 to 2.67 indeterminate, above 2.67 high — and uses the 2.0 lower cut-off at age 65 or older. With the upper limit of normal for AST from your report it also gives APRI, the AST-to-platelet ratio index. Platelets can be entered in × 10⁹/L, per µL or lakh per µL. Nothing you type leaves your browser.

Without a pass, the free preview shows the FIB-4 in full with its risk band and every caution, and the first row of the working table; a Pro pass unlocks APRI, every other figure and Copy result.

Common uses

• Checking the risk of advanced liver fibrosis in fatty liver disease (NAFLD, now called MASLD) from routine blood tests.
• Deciding with a doctor whether a second test such as elastography is needed.
• Following FIB-4 over the years in people with diabetes or other metabolic risk factors.
• Working out APRI from the same blood test.

The formulas and cut-offs

• FIB-4 = (age in years × AST in U/L) ÷ (platelets in 10⁹/L × √ALT in U/L).
• Risk of advanced fibrosis (AASLD practice guidance for fatty liver disease): below 1.3 low — follow up in primary care and repeat the test over the years; 1.3 to 2.67 indeterminate — a second test, preferably vibration-controlled elastography or the ELF blood test; above 2.67 high — referral to gastroenterology or hepatology should be considered. At 65 or older the lower cut-off is 2.0, derived and validated in a European multicentre cohort because specificity fell too low with 1.3.
• Cirrhosis (the same guidance): FIB-4 of 3.48 or more had 90% specificity, below 1.67 90% sensitivity.
• APRI = (AST ÷ upper limit of normal × 100) ÷ platelets in 10⁹/L. The WHO hepatitis B guidelines list a low cut-off that rules out and a high cut-off that rules in: 0.5 and 1.5 for significant fibrosis, 1.0 and 2.0 for cirrhosis. For deciding hepatitis B treatment, the same guidelines count an APRI above 0.5 as evidence of significant fibrosis and above 1 as evidence of cirrhosis, because the older cut-off of 2 missed at least half of the people with cirrhosis.

FIB-4 was first developed in people with HIV and hepatitis C, where its cut-offs were 1.45 and 3.25.

When FIB-4 is less reliable

• Under 35: accuracy is low, so a second test may be needed even with a low score when there are metabolic risk factors or raised liver enzymes.
• 65 or older: with the 1.3 cut-off the specificity was only 35%, so many people without advanced fibrosis scored above it; the 2.0 cut-off reduces these false alarms.
• Acute illness: FIB-4 is not used in acutely ill patients.
• Diabetes: the scores can perform less well, and the test is usually repeated every 1–2 years.

A FIB-4 estimates risk; it does not diagnose fibrosis or cirrhosis, and a liver specialist may use elastography, other blood tests or a biopsy.

Sources

• Sterling RK et al. Development of a simple noninvasive index to predict significant fibrosis in patients with HIV/HCV coinfection — Hepatology
• Rinella ME et al. AASLD Practice Guidance on the clinical assessment and management of nonalcoholic fatty liver disease — Hepatology
• McPherson S et al. Age as a confounding factor for the accurate non-invasive diagnosis of advanced NAFLD fibrosis — Am J Gastroenterol
• Wai CT et al. A simple noninvasive index can predict both significant fibrosis and cirrhosis in patients with chronic hepatitis C — Hepatology
• Guidelines for the prevention, diagnosis, care and treatment for people with chronic hepatitis B infection — WHO: the APRI cut-offs (Table 4.3) and treatment thresholds
• Rinella ME et al. A multisociety Delphi consensus statement on new fatty liver disease nomenclature — Hepatology: NAFLD renamed MASLD

Limitations

• Estimates risk only: it does not diagnose fibrosis or cirrhosis.
• Less accurate under 35 and in diabetes; not for acutely ill patients.
• The bands are those for fatty liver disease; other liver diseases use other cut-offs.
• Accepts age 18–110 years, AST and ALT 1–5,000 U/L and platelets 5–2,000 × 10⁹/L.

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