APRI Calculator
APRI score from AST, the AST upper limit, and platelets for fibrosis risk bands.
What it does
APRI stands for AST to platelet ratio index. It is a simple blood-based score that estimates the likelihood of significant liver fibrosis and cirrhosis.
The index divides AST by its laboratory upper limit of normal, then multiplies by 100 divided by the platelet count. Using the upper limit of normal makes the score portable across laboratories, but the result still depends on the reference range used.
APRI was studied most extensively in chronic hepatitis C and chronic hepatitis B. The World Health Organization uses 0.5 and 1.0 as reference thresholds in its chronic hepatitis B guidance, while other causes of liver disease may use different cutoffs.
The defaults show AST 64 U/L, an upper limit of 40 U/L, and platelets 180 x 10^9/L. The score is 0.89, above the significant fibrosis threshold but at or below the cirrhosis threshold.
How to use
- Enter AST in U/L from the current blood panel.
- Enter the AST upper limit of normal from the same laboratory report.
- Enter the platelet count in x 10^9/L.
- Press Calculate to obtain the APRI score.
- Compare the score with the 0.5 and 1.0 reference thresholds.
- Interpret the result with the cause of liver disease, liver enzymes, imaging, and clinical findings.
Formula
- AST
- Aspartate aminotransferase in U/L.
- AST ULN
- The laboratory's upper limit of normal for AST in U/L.
- platelets
- Platelet count in x 10^9/L.
Divide AST by the upper limit of normal, divide 100 by the platelet count, then multiply the two ratios. A platelet count of 180 x 10^9/L is entered as 180, not 180,000. The 0.5 and 1.0 thresholds come from the WHO chronic hepatitis B framework; they are not universal cutoffs for every cause of liver disease.
Worked example
Example: AST 64, AST upper limit 40, platelets 180
Defaults: AST 64 U/L, AST upper limit of normal 40 U/L, platelet count 180 x 10^9/L.
- Divide AST by the upper limit: 64 / 40 = 1.6.
- Divide 100 by platelets: 100 / 180 = 0.5556.
- Multiply the ratios: 1.6 x 0.5556 = 0.8889.
- Round to two decimals: APRI = 0.89.
- The result is above 0.5 and at or below 1.0, so it is above the significant fibrosis threshold but not above the cirrhosis threshold.
- The tool reports 0.89 and suggests fibrosis assessment with elastography where available.
Reference table
| APRI result | Interpretation |
|---|---|
| 0.5 or less | Below the significant fibrosis threshold |
| Above 0.5 to 1.0 | Above the significant fibrosis threshold |
| Above 1.0 | Above the cirrhosis threshold |
Limits
- APRI is a screening and risk-stratification tool, not a substitute for elastography or biopsy.
- The score is less reliable when AST is only mildly elevated or when platelets are affected by another condition.
- Cutoffs differ by cause of liver disease and by guideline; the 0.5 and 1.0 values are not universal.
- Laboratory differences in the AST upper limit of normal can change the score.
Common mistakes
- Entering platelets as 180,000 instead of 180 x 10^9/L.
- Using a generic AST upper limit instead of the value from the same laboratory.
- Applying the WHO hepatitis B thresholds to every cause of liver disease without checking the relevant guidance.
- Treating APRI above 1.0 as a confirmed diagnosis of cirrhosis.
- Ignoring other causes of thrombocytopenia or elevated AST.
Try it yourself
Quick checks. Answers sit tucked under each question.
What is APRI for AST 60 U/L, AST upper limit 40 U/L, and platelets 200 x 10^9/L?
0.75. The calculation is (60 / 40) x (100 / 200) = 1.5 x 0.5. This is above 0.5 and at or below 1.0.
What is APRI for AST 120 U/L, AST upper limit 40 U/L, and platelets 100 x 10^9/L?
3.00. The calculation is (120 / 40) x (100 / 100) = 3 x 1. This is above the cirrhosis threshold.
What is APRI for AST 30 U/L, AST upper limit 40 U/L, and platelets 250 x 10^9/L?
0.30. The calculation is (30 / 40) x (100 / 250) = 0.75 x 0.4. This is below the significant fibrosis threshold.
Questions
What does APRI stand for?
AST to platelet ratio index. It compares AST with its upper limit of normal and with the platelet count.
What is a normal APRI score?
There is no single normal value. In the WHO chronic hepatitis B framework, 0.5 or less is below the significant fibrosis threshold, while higher values raise concern.
Can APRI diagnose cirrhosis?
No. A score above 1.0 raises concern and usually prompts further assessment. Cirrhosis is diagnosed from imaging, elastography, laboratory markers, and clinical findings, sometimes with biopsy.
Why does the AST upper limit matter?
AST is divided by the upper limit, so using a different reference range changes the score. Use the limit printed by the laboratory that measured the AST.
Is APRI better than FIB-4?
Neither is universally better. FIB-4 includes age and ALT, while APRI relies on AST and platelets. Performance depends on the population and the cause of liver disease.
Does APRI require fasting?
No. It uses routine AST and platelet results. Trends are easier to interpret when tests come from the same laboratory.
Sources
- WHO guidelines for chronic hepatitis B, 2024
- WHO chronic hepatitis B guideline PDF
- Wai et al., simple noninvasive index for chronic hepatitis C