🫁 FIB-4 / APRI Calculator Non-Invasive Liver Fibrosis
Compute both FIB-4 and APRI in one click from age, AST, ALT, and platelets.
ℹ️ For educational and reference use only. Does not replace professional medical diagnosis or treatment.
Years
Units: U/L
Units: U/L
Units: ×10⁹/L (× 1,000/μL)
Units: U/L (varies by lab; default 40)
📊 Results
📋 FIB-4 Reference
| Category | FIB-4 | Interpretation |
|---|---|---|
| Low risk | < 1.30 | Advanced fibrosis unlikely |
| Indeterminate | 1.30 – 2.67 | Additional testing needed (VCTE, MRE) |
| High risk | > 2.67 | Advanced fibrosis (F3–F4) likely |
📋 APRI Reference
| Category | APRI | Interpretation |
|---|---|---|
| Low risk | < 0.5 | Significant fibrosis unlikely |
| Indeterminate | 0.5 – 1.5 | Additional testing needed |
| High risk | > 1.5 | Cirrhosis likely |
📐 Formulas
FIB-4 (Fibrosis-4 Index)
FIB-4 = (Age × AST) / (PLT × √ALT)
* Age in years; AST/ALT in U/L; PLT in ×10⁹/L
APRI (AST to Platelet Ratio Index)
APRI = (AST / ULN) / PLT × 100
* ULN = AST upper limit of normal (default 40 U/L; varies by lab)
FIB-4 = (Age × AST) / (PLT × √ALT)
* Age in years; AST/ALT in U/L; PLT in ×10⁹/L
APRI (AST to Platelet Ratio Index)
APRI = (AST / ULN) / PLT × 100
* ULN = AST upper limit of normal (default 40 U/L; varies by lab)
❓ Frequently Asked Questions
What is FIB-4? ▼
Developed by Sterling et al. (2006) in HIV/HCV coinfection, FIB-4 combines age, AST, ALT, and platelets to screen for advanced liver fibrosis non-invasively. It is AASLD and EASL first-line recommendation in NAFLD/MASLD.
What is APRI? ▼
Developed by Wai et al. (2003), APRI uses only AST and platelets. WHO recommends it for HBV/HCV screening in low-resource settings because of its simplicity.
FIB-4 vs APRI? ▼
FIB-4 typically has higher AUROC. Both are screens — indeterminate results should proceed to transient elastography (FibroScan/VCTE), MRE, or biopsy for confirmation.
Limitations of FIB-4? ▼
Underestimates in age < 35 and overestimates in age > 65 because of the age multiplier. Also inaccurate when AST is elevated from non-hepatic causes (hemolysis, muscle injury) or when platelets are low for other reasons (ITP, splenomegaly unrelated to liver).
🔗 Related Calculators
⚠️ Disclaimer — Educational reference only. Confirm elevated scores with transient elastography (VCTE/FibroScan), MRE, or biopsy before clinical decisions.
References: Sterling RK et al. Hepatology. 2006;43(6):1317-1325. · Wai CT et al. Hepatology. 2003;38(2):518-526. · AASLD 2023 NAFLD Guidance. · EASL 2021 HCV Guideline.
References: Sterling RK et al. Hepatology. 2006;43(6):1317-1325. · Wai CT et al. Hepatology. 2003;38(2):518-526. · AASLD 2023 NAFLD Guidance. · EASL 2021 HCV Guideline.