FIB-4 and APRI Calculator: Liver Fibrosis Indices

FIB-4 (Sterling 2006) uses age, AST, ALT and platelets. AASLD 2023 thresholds concern the likelihood of advanced fibrosis in metabolic fatty liver disease, not fibrosis staging. Ages 35–65: lower threshold 1.3; over 65: 2.0; upper threshold 2.67. No category is assigned below 35; do not interpret during acute illness. APRI (Wai 2003) and thresholds 0.5/1.5 concern significant fibrosis in chronic hepatitis C and do not automatically transfer to other diseases.

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Calculation

The AST upper limit of normal from your lab report; usually 35–40 U/L.

The result updates as you change the fields. Your data never leaves the browser.

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.

Result

FIB-4
1.27 index

Low risk < 1.3; gray zone up to 2.67; high risk > 2.67

Interpretation
Below the assessment threshold: a low result does not exclude all liver disease
APRI
0.45 · significant fibrosis unlikely index

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) uses age, AST, ALT and platelets. AASLD 2023 thresholds concern the likelihood of advanced fibrosis in metabolic fatty liver disease, not fibrosis staging. Ages 35–65: lower threshold 1.3; over 65: 2.0; upper threshold 2.67. No category is assigned below 35; do not interpret during acute illness. APRI (Wai 2003) and thresholds 0.5/1.5 concern significant fibrosis in chronic hepatitis C and do not automatically transfer to other diseases. 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.

How it is calculated

FIB-4 (Sterling 2006) uses age, AST, ALT and platelets. AASLD 2023 thresholds concern the likelihood of advanced fibrosis in metabolic fatty liver disease, not fibrosis staging. Ages 35–65: lower threshold 1.3; over 65: 2.0; upper threshold 2.67. No category is assigned below 35; do not interpret during acute illness. APRI (Wai 2003) and thresholds 0.5/1.5 concern significant fibrosis in chronic hepatitis C and do not automatically transfer to other diseases.

Formula

FIB-4 = age × AST / (platelets × √ALT); APRI = (AST / AST_ULN) × 100 / platelets. FIB-4 (Sterling 2006) uses age, AST, ALT and platelets. AASLD 2023 thresholds concern the likelihood of advanced fibrosis in metabolic fatty liver disease, not fibrosis staging. Ages 35–65: lower threshold 1.3; over 65: 2.0; upper threshold 2.67. No category is assigned below 35; do not interpret during acute illness. APRI (Wai 2003) and thresholds 0.5/1.5 concern significant fibrosis in chronic hepatitis C and do not automatically transfer to other diseases.

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

How to use the calculation

1

Enter the starting values

FIB-4 (Sterling 2006) uses age, AST, ALT and platelets. AASLD 2023 thresholds concern the likelihood of advanced fibrosis in metabolic fatty liver disease, not fibrosis staging. Ages 35–65: lower threshold 1.3; over 65: 2.0; upper threshold 2.67. No category is assigned below 35; do not interpret during acute illness. APRI (Wai 2003) and thresholds 0.5/1.5 concern significant fibrosis in chronic hepatitis C and do not automatically transfer to other diseases.

2

Adjust the parameters

FIB-4 = age × AST / (platelets × √ALT); APRI = (AST / AST_ULN) × 100 / platelets. FIB-4 (Sterling 2006) uses age, AST, ALT and platelets. AASLD 2023 thresholds concern the likelihood of advanced fibrosis in metabolic fatty liver disease, not fibrosis staging. Ages 35–65: lower threshold 1.3; over 65: 2.0; upper threshold 2.67. No category is assigned below 35; do not interpret during acute illness. APRI (Wai 2003) and thresholds 0.5/1.5 concern significant fibrosis in chronic hepatitis C and do not automatically transfer to other diseases.

3

Read the result

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.

Frequently asked questions

What does the calculation show?

FIB-4 (Sterling 2006) uses age, AST, ALT and platelets. AASLD 2023 thresholds concern the likelihood of advanced fibrosis in metabolic fatty liver disease, not fibrosis staging. Ages 35–65: lower threshold 1.3; over 65: 2.0; upper threshold 2.67. No category is assigned below 35; do not interpret during acute illness. APRI (Wai 2003) and thresholds 0.5/1.5 concern significant fibrosis in chronic hepatitis C and do not automatically transfer to other diseases.

What limitations apply?

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.

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