FIB-4 Calculator

Enter age, AST, ALT, and platelet count to calculate the FIB-4 (Fibrosis-4) index — FIB-4 = (Age × AST) ÷ (Platelets × √ALT) — and see the standard low/indeterminate/high liver-fibrosis risk band.

Quick Facts

Formula
FIB-4 = (Age × AST) ÷ (Platelets × √ALT)
Platelets in ×10⁹/L (same number as on a standard CBC, e.g. 200).
Low probability cutoff
FIB-4 < 1.45
Advanced fibrosis (F3-F4) is unlikely.
High probability cutoff
FIB-4 > 3.25
Suggests advanced fibrosis; specialist follow-up recommended.
Origin
Sterling et al., 2006
Originally validated in HIV/HCV co-infected patients; now widely used in NAFLD.

Your Results

Calculated
FIB-4 Score
-
(Age × AST) ÷ (Platelets × √ALT)
Fibrosis Risk Category
-
Based on Sterling et al. cutoffs
AST/ALT Ratio (De Ritis)
-
Supplementary marker, not part of FIB-4
Suggested Next Step
-
Educational guidance only

Ready

Enter your age, AST, ALT, and platelet count, then press Calculate. This tool is educational and does not replace medical advice.

Understanding the FIB-4 Index (Fibrosis-4 Score)

The FIB-4 (Fibrosis-4) index is a validated, noninvasive score used to estimate the likelihood of advanced liver fibrosis (scarring) from routine blood work. It was derived by Sterling and colleagues (2006) in patients with chronic hepatitis C/HIV co-infection and has since been widely adopted for chronic hepatitis B and non-alcoholic fatty liver disease (NAFLD/NASH) as a first-line, low-cost triage tool that helps decide who may need further testing, such as elastography (FibroScan) or a liver biopsy, and who can be safely monitored in primary care.

How the FIB-4 score is calculated

FIB-4 combines four routinely available values into one formula: FIB-4 = (Age × AST) ÷ (Platelet count × √ALT). Age is in years; AST (aspartate aminotransferase) and ALT (alanine aminotransferase) are liver enzyme levels in U/L from a standard liver panel; and platelet count is entered in ×10⁹/L — the same number your lab report shows (for example, enter 200, not 200,000). A higher AST relative to ALT and platelets, combined with older age, pushes the score up, which is consistent with the biological picture of advancing fibrosis: enzyme patterns shift and platelet counts fall as portal hypertension develops.

Interpreting your FIB-4 result

Using the original Sterling et al. thresholds: a score below 1.45 indicates a low probability of advanced fibrosis (F3-F4) and generally rules out significant scarring; a score above 3.25 indicates a high probability of advanced fibrosis and typically warrants hepatology referral; and scores in the 1.45-3.25 indeterminate zone are inconclusive and usually call for a second-line test such as transient elastography or specialist assessment. Some NAFLD-specific guidelines use tighter cutoffs (roughly 1.30 and 2.67) to optimize sensitivity in that population — your clinician will know which threshold applies to your situation.

Limitations and when to see a specialist

FIB-4 is a screening estimate, not a diagnosis. It can be less reliable at the extremes of age — it tends to overestimate fibrosis risk in people over 65 and underestimate it in those under 35 — and it was not designed for patients with acute hepatitis, other causes of thrombocytopenia, or advanced kidney disease. Always discuss an indeterminate or high result with a physician or hepatologist; this calculator is for education only and is not a substitute for professional medical advice, diagnosis, or treatment.

Frequently Asked Questions

What is the FIB-4 score used for?
FIB-4 (Fibrosis-4 index) is a noninvasive screening score that estimates the probability of advanced liver fibrosis (scarring) using age, AST, ALT, and platelet count. It is widely used in chronic hepatitis C, hepatitis B, and non-alcoholic fatty liver disease (NAFLD/NASH) to decide who may need further liver evaluation.
What do FIB-4 cutoff values mean?
Using the original Sterling et al. thresholds, a FIB-4 below 1.45 suggests a low probability of advanced fibrosis, above 3.25 suggests a high probability, and 1.45-3.25 is an indeterminate zone that usually calls for further testing such as elastography (FibroScan) or specialist referral.
What lab values do I need to calculate FIB-4?
You need your age in years, AST (aspartate aminotransferase) and ALT (alanine aminotransferase) in U/L from a liver panel, and platelet count in ×10⁹/L (the same number reported on a standard CBC, e.g. 200, not 200,000).
Is a FIB-4 result a diagnosis of liver disease?
No. FIB-4 is a risk-stratification and screening estimate, not a diagnosis. It can be less reliable in patients over 65 or under 35 and in those with normal ALT. An abnormal or indeterminate result should be discussed with a physician or hepatologist, who may recommend imaging, elastography, or biopsy.

Related calculators