FIB-4 and APRI Calculator: Liver Fibrosis Indices
FIB-4 and APRI from age, AST, ALT and platelets, with thresholds and limitations for discussion with a clinician.
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Calculation
Result
- FIB-4
- 1.27 index
- Interpretation
- Below the assessment threshold: a low result does not exclude all liver disease
- APRI
- 0.45 · significant fibrosis unlikely index
Low risk < 1.3; gray zone up to 2.67; high risk > 2.67
Thresholds of 0.5 and 1.5 concern significant fibrosis in chronic hepatitis C; they do not assign a fibrosis stage.
FIB-4: Sterling 2006, age-adjusted thresholds for metabolic fatty liver disease; APRI: Wai 2003, chronic hepatitis C. Do not interpret FIB-4 during acute illness. Reference ranges are population benchmarks from the cited sources. Laboratories use their own ranges, and interpretation depends on clinical context: discuss the result with your physician.
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How it is calculated
FIB-4 (Sterling, 2006) combines age, AST, ALT and platelets. In metabolic fatty liver disease pathways, a low result helps identify a lower likelihood of advanced fibrosis; intermediate or high results need further assessment. It is neither a fibrosis stage nor a diagnosis. APRI (Wai, 2003) was developed for chronic hepatitis C; its thresholds do not automatically transfer to other diseases.
Formula
FIB-4 = Age (years) × AST (U/L) / [ Platelets (10⁹/L) × √ALT (U/L) ] APRI = [ AST / AST ULN ] × 100 / Platelets (10⁹/L) FIB-4 cut-offs: < 1.3 (< 2.0 at age ≥ 65) low risk; 1.3–2.67 indeterminate; > 2.67 high APRI cut-offs: < 0.5 low; > 1.5 significant fibrosis likely
Limits of the method
FIB-4 helps estimate the likelihood of advanced fibrosis but cannot confirm or exclude it in every individual. Accuracy is low below age 35; do not interpret it during acute illness. Non-liver causes of low platelets and muscle-related AST elevation can distort the result. Thresholds depend on age, disease cause and clinical context.
Sources of the method
- Sterling R.K. et al. Development of a simple noninvasive index to predict significant fibrosis in patients with HIV/HCV coinfection. Hepatology, 2006;43(6):1317–1325
- Wai C.T. et al. A simple noninvasive index can predict both significant fibrosis and cirrhosis in patients with chronic hepatitis C. Hepatology, 2003;38(2):518–526
- EASL Clinical Practice Guidelines on non-invasive tests for evaluation of liver disease severity and prognosis — 2021 update. J Hepatol, 2021;75(3):659–689
This calculation is for reference only and is not medical advice, a diagnosis or a prescription. If you have a medical condition, are pregnant, take medication or have any doubts, discuss the result with a physician or a qualified nutrition professional.
How to assess liver fibrosis from labs
Take AST, ALT and platelets
Transaminases from chemistry, platelets from the blood count. The tests should be from the same period (within 1–2 weeks) and outside acute illness.
Enter age and the AST ULN
FIB-4 depends on age: after 65 the low-risk cut-off rises to 2.0. APRI needs your lab’s AST upper limit of normal.
Follow the algorithm
Low FIB-4 — monitoring and risk-factor control. Gray zone — elastography. High — hepatologist. This is the official EASL/AASLD pathway for NAFLD.
FIB-4 worked examples
Age 52, AST 38, ALT 55, platelets 210
FIB-4 of 1.27 is below 1.3; APRI is 0.45 with an AST ULN of 40 U/L. The result does not exclude steatosis or inflammation; follow-up depends on clinical context.
Age 61, AST 62, ALT 48, platelets 150
AST above ALT and reduced platelets are signs of progression. FIB-4 above 2.67 with APRI 1.03: elastography and a hepatologist are needed to exclude F3–F4.
Age 68, AST 95, ALT 60, platelets 95
FIB-4 is 8.78 and APRI is 2.50 with an AST ULN of 40 U/L. The result remains high with the age-adjusted threshold of 2.0, but does not confirm cirrhosis: clinical assessment is needed.
Why FIB-4 became the first-line test
FIB-4 uses readily available tests and is therefore included in first-stage assessment pathways for metabolic fatty liver disease. Its purpose is to help choose further evaluation, not replace elastography or assign a stage from one number. Predictive value depends on disease prevalence in the population assessed.
The gray zone: what to do at FIB-4 between 1.3 and 2.67
An intermediate score does not confirm fibrosis. A clinician may choose elastography or an ELF test and interpret it alongside the cause of disease, laboratory results and symptoms. Repeat testing intervals depend on risk factors.
Interpreting FIB-4 and APRI
| FIB-4 | APRI | Approach |
|---|---|---|
| < 1.3 (< 2.0 after 65) | < 0.5 | Advanced fibrosis unlikely; risk-factor control, recalculate in 1–3 years |
| 1.3–2.67 (2.0–2.67 from age 65) | 0.5–1.5 | Indeterminate: elastography (FibroScan), ELF test |
| > 2.67 | > 1.5 | High F3–F4 risk: hepatology consultation, elastography, further work-up |
| > 3.25 | > 2.0 | High values need assessment; these indices do not establish fibrosis stage or cirrhosis |
The columns show separate guide values, not a combined diagnostic score. FIB-4 thresholds concern metabolic fatty liver disease; APRI thresholds concern chronic hepatitis C. FIB-4 has low accuracy below age 35 and should not be used in acute illness.
Frequently asked questions
What is a normal FIB-4?
A value below 1.3 (below 2.0 at age 65 and older) is considered low risk of advanced fibrosis. That is not a "normal liver" — steatosis and inflammation are possible at that index, but scarring to stage F3–F4 is unlikely.
Can FIB-4 be high without liver disease?
Yes: thrombocytopenia of another cause, AST elevation after exercise or from muscle disease, older age without the adjusted cut-off. That is why a high index is a reason for elastography, not a diagnosis.
How does APRI differ from FIB-4?
APRI uses only AST and platelets and was developed for hepatitis C. FIB-4 adds age and ALT and is more accurate in NAFLD. Fatty-liver guidelines recommend FIB-4; APRI is useful as a second reference in viral hepatitis.
What is elastography and why after FIB-4?
Elastography measures liver stiffness. It can refine risk assessment after FIB-4, but is also affected by inflammation and clinical context; it does not always establish a fibrosis stage by itself.
Is liver fibrosis reversible?
Stages F1–F3 are partly reversible once the cause is removed: 10% weight loss in NAFLD, alcohol abstinence, treatment of viral hepatitis. Even in cirrhosis progression can be halted. FIB-4 over time helps see the effect.
Who should calculate FIB-4 regularly?
Everyone with type 2 diabetes, obesity, metabolic syndrome, steatosis on ultrasound, elevated transaminases, chronic hepatitis and regular alcohol use. ADA and EASL recommend recalculating yearly or every 2–3 years depending on risk.
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What next
Formula breakdowns, biomarker reference ranges and nutrition articles with cited sources are in the NutriFit knowledge base.
Go to the knowledge base