FIB-4 Calculator

Created by Łucja Zaborowska, MD, PhD candidate
Last updated: Nov 30, 2021

This FIB-4 calculator is a simple tool for assessing the probability of NAFLD liver fibrosis.

FIB-4 score is a powerful instrument for ruling out or confirming a diagnosis of advanced fibrosis. It's most efficient in adults aged 35-65.

We decided to add the functionality of the APRI calculator, so you can get a more complete assessment for your liver's condition. Check the advanced mode button to see this part of the calculator.

➡️Read on to discover the full interpretation of your results for both the FIB-4 index and the APRI score.⬅️

How to use the FIB-4 calculator

To use our F4 fibrosis tool, you'll need to prepare the following blood tests results:

  • AST - usually given in U/L (also called: aspartate transaminase/ AspAT/ ASAT/ AAT/ GOT/ SGOT);
  • ALT - usually given in U/L (alanine transaminase / alanine aminotransferase/ ALAT/ SGPT); and
  • Platelet count - you can find either the number of platelets per mm³, the number of platelets per μL, or the number of platelets * 10⁹ per liter.

Remember, our FIB-4 calculator works best for people aged 35-65 years old.
People outside of this bracket may receive a false-positive result.

💡False positive - a situation where a healthy person receives a result that strongly suggests that they are sick.

Check our other calculators to assess various functions of your liver:

Fibrosis-4 score meaning

FIB-4 is used mostly for people with NAFLD (read below), and HCV, HBV, or HIV co-infections. It is a non-invasive fibrosis and subsequent loss of liver function assessment.

  • FIB-4 > 3.25 - confirms the presence of fibrosis in 82.1% of patients; and
  • FIB-4 > 1.45 - excludes the presence of fibrosis in 94.7% of patients.

NAFLD is an abbreviation for Non-Alcoholic Fatty Liver Disease. NAFLD is the most common liver disease worldwide - it's a condition that, may, over time, lead to an irreversible cirrhosis of the liver, and a permanent loss of liver function. In comparison to NASH (Non-Alcoholic SteatoHepatitis), NAFLD does not consist of liver inflammation. The reasons NAFLD and NASH develop include:

  • Obesity;
  • Metabolic syndrome (connected with obesity, includes, for example, hypertension or type 2 diabetes);
  • Drugs, toxins; and
  • Inherited metabolic diseases.

Liver damage, such as cirrhosis or inflamation, is also caused by the chronic intake of too many units of alcohol. The Audit-C test may be helpful in screening those potentially at risk.

Don't hesitate to ask for professional help if you think you may need it.

How to calculate the FIB-4 liver fibrosis score?

The NAFLD fibrosis score can be presented in a single equation:

FIB-4 = (age * AST) / ( platelet count * √ALT)

Note, that the ALT levels need to be square rooted!

APRI score

The APRI ratio is a simple way to assess the probability of fibrosis progression among patients suffering from hepatitis type C. Check the advanced mode button!

The APRI formula is as follows:

APRI = (AST / upper limit of normal AST) / platelet count

*Most experts suggest using the value of 40 U/L as the upper normal AST level limit - we also decided to use this value in our calculator.


A value of ≥1 means that there is a high possibility of severe cirrhosis. In general, a high APRI value indicates an increased risk of disease progression.

A value <0.5 can rule out the possibility of progression in around 87% of cases.

Other fibrosis scores

Apart from the FIB-4 or APRI score, we use plenty of different fibrosis scores to asses the probability of the liver disease, with varying levels of invasivity. Let's enumerate a few of them:

Łucja Zaborowska, MD, PhD candidate
Platelet count
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