FIB-4 Index Calculator.
FIB-4 is the first-line, non-invasive screen for advanced liver fibrosis in fatty liver disease. It needs only four routine values — age, AST, ALT, and platelets — no biopsy.
The first-line fatty-liver fibrosis screen.
Fatty liver disease (MASLD) is common and usually harmless until it scars (fibrosis). The question that matters is who has advanced fibrosis — and biopsy is invasive. FIB-4 answers it from four routine numbers: age, AST, ALT, and platelet count, combined as (age × AST) / (platelets × √ALT). Its real strength is ruling fibrosis out: below the low cut-point it has a high negative predictive value.
Interpretation has three zones — low (<1.3), indeterminate (1.3–2.67), and high (>2.67) — and the low cut-point rises to 2.0 after age 65, because FIB-4 drifts up with age and otherwise over-calls. An indeterminate or high score is a prompt for a second-line test (elastography/FibroScan or an ELF panel), not a diagnosis on its own.
- Sterling RK, Lissen E, Clumeck N, et al. (2006). Development of a simple noninvasive index to predict significant fibrosis in HIV/HCV coinfection. Hepatology, 43(6), 1317–1325.
- McPherson S, Hardy T, Dufour JF, et al. (2017). Age as a confounding factor for the accurate non-invasive diagnosis of advanced NAFLD fibrosis. Am J Gastroenterol, 112(5), 740–751.
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