Health calculators

FIB-4 Liver Fibrosis Calculator

Calculate the FIB-4 index, a score from four routine results (age, AST, ALT and platelet count) used to estimate the chance of advanced liver scarring.

Same number as ×10³/µL

What FIB-4 is

FIB-4 was developed from routine blood tests in 832 people with HIV and hepatitis C coinfection who had liver biopsies. It combines age, AST, ALT and platelet count: age multiplied by AST, divided by the platelet count multiplied by the square root of ALT.1

How to read the result

In the original study, a value below 1.45 ruled out advanced fibrosis with a negative predictive value of 90% (sensitivity 70%), and a value above 3.25 had a positive predictive value of 65% with 97% specificity; using these two cutoffs, biopsy could have been avoided in 71% of the validation group.1 In 541 adults with fatty liver disease, FIB-4 identified advanced fibrosis better than the other simple scores tested (area under the curve 0.802, against 0.768 for the NAFLD fibrosis score).2 Cutoffs for fatty liver disease differ from the original ones, which is why this page shows the original figures with their source rather than a single universal threshold.

Age changes the picture

FIB-4 was developed and validated mainly in people aged 35 to 65. At 35 or younger it performed poorly (area under the curve 0.60). At 65 or older its specificity fell to 35%, producing many false positives; a cutoff of 2.0 for this age group improved specificity to 70% while keeping sensitivity at 77%.3

How we check this calculator

The page uses the published formula exactly. Every time the site is built, an automated test compares our code with an independent implementation across 108 combinations of age and lab values; the build fails if any result differs.

This calculator is for education. A FIB-4 result is an estimate, not a diagnosis; your clinician will interpret it alongside other tests, such as liver stiffness imaging, and your history.

References

  1. 1Sterling RK, et al. "Development of a simple noninvasive index to predict significant fibrosis in patients with HIV/HCV coinfection." Hepatology. 2006;43(6):1317-25. PubMed · DOI
  2. 2Shah AG, et al. "Comparison of noninvasive markers of fibrosis in patients with nonalcoholic fatty liver disease." Clin Gastroenterol Hepatol. 2009;7(10):1104-12. PubMed · DOI
  3. 3McPherson S, 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 · DOI