Liver
FIB-4 calculator for liver fibrosis
Estimate the FIB-4 index from age, AST, ALT, and platelet count, with the age-adjusted lower cutoff applied automatically, and see how the score is used to triage advanced liver fibrosis.
Enter your values above to see your result and what it means.
What FIB-4 is for
FIB-4 is a triage test. It combines four values already present on routine bloods to sort people with suspected fatty liver disease into those who can be reassured and rechecked, and those who need a better fibrosis test such as elastography. It was originally developed and validated in HIV and hepatitis C coinfection, and has since been adopted widely in non-alcoholic and metabolic-associated fatty liver pathways because it costs nothing to calculate.
The age problem, stated plainly
Age multiplies the numerator of the formula, so FIB-4 rises as people get older whether or not their liver changes. McPherson and colleagues showed that applying the standard 1.30 lower cutoff above roughly age 65 produces a high false-positive rate, and recommended raising it to about 2.0 in that group. This calculator applies that adjustment automatically and tells you when it has, because reporting an unadjusted indeterminate result to a 70-year-old presents an artefact of the formula as a clinical finding.
What can distort the score
Anything that lowers platelets independently of the liver, including immune thrombocytopenia and some medicines, will push FIB-4 up. Acute hepatitis of any cause raises the transaminases sharply and makes the index unreliable, so it should be calculated on stable values rather than during an acute illness. Alcohol-related liver disease characteristically raises AST relative to ALT, which also lifts the score.
Frequently asked questions
What is a normal FIB-4 score?
Below 1.30 is the conventional low-risk threshold for adults under 65, and it makes advanced fibrosis unlikely. Above 2.67 is the high-risk threshold. Between the two is indeterminate, and a large share of people tested fall in that middle band.
Why does the cutoff change at 65?
Age is in the numerator of the formula, so the score rises with age by construction. In people aged 65 and over, the 1.30 cutoff misclassifies a high proportion as indeterminate or high risk, so a raised lower cutoff of around 2.0 is recommended. This calculator applies it automatically and says so in the result.
Does a high FIB-4 mean I have cirrhosis?
No. FIB-4 estimates the probability of advanced fibrosis and is used to decide who needs a better test. A high score means elastography or specialist assessment is indicated, and a meaningful proportion of people above the threshold turn out not to have advanced fibrosis.
My platelet count is written as ×10³/µL. Is that different?
No, it is the same number. A platelet count of 220 ×10⁹/L is identical to 220 ×10³/µL, so enter it as it appears on your report.
Sources
- Sterling RK, Lissen E, Clumeck N, et al. Development of a simple noninvasive index to predict significant fibrosis in patients with HIV/HCV coinfection. Hepatology. 2006;43(6):1317-1325.
- McPherson S, Hardy T, Dufour JF, 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.