Fibrosis 4 FIB 4 Calculator

FIB 4 index Explanation and Clinical Context The FIB 4 index is a noninvasive score that estimates the probability of advanced liver fibrosis using routinely available values including patient age AST ALT and platelet count. It is calculated as age in years multiplied by AST in U per L divided by platelet count in 10 to the power of 9 per L times the square root of ALT in U per L. Commonly used cutoffs are less than 1.45 to suggest low probability of advanced fibrosis between 1.45 and 3.25 as an indeterminate zone that warrants further evaluation and greater than 3.25 to suggest high probability of advanced fibrosis.

Clinicians use FIB 4 as an initial triage tool in primary care and specialty settings to identify patients who can be reassured and those who need further noninvasive tests or referral for elastography or specialist assessment. The score performs best as part of a sequential diagnostic algorithm combined with other tests and clinical context rather than in isolation. Reference EASL Clinical Practice Guidance on non invasive tests for evaluation of liver disease severity and prognosis 2021.

MDCalc Fibrosis 4 calculator reference page. Review and validation studies in PubMed Central discuss accuracy and limitations of FIB 4 in various populations. Practical clinical summary in Singapore Medical Journal on use of FIB 4 in clinical practice.