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FIB-4 Calculator

Created by Łucja Zaborowska, MD, PhD candidate
Reviewed by Bogna Szyk, Jack Bowater and Aleksandra Zając, MD
Based on research by
Richard K. Sterling, Eduardo Lissen, Nathan Clumeck, Ricard Sola, Mendes Cassia Correa, Julio Montaner, Mark S. Sulkowski, Francesca J. Torriani, Doug T. Dieterich, David L. Thomas, Diethelm Messinger, Mark Nelson Development of a simple noninvasive index to predict significant fibrosis in patients with HIV/HCV coinfection; Hepatology; May 2006See 1 more source
Beom Kyung Kim 1, Do Young Kim, Jun Yong Park, Sang Hoon Ahn, Chae Yoon Chon, Ja Kyung Kim, Yong Han Paik, Kwan Sik Lee, Young Nyun Park, Kwang Hyub Han Validation of FIB-4 and comparison with other simple noninvasive indices for predicting liver fibrosis and cirrhosis in hepatitis B virus-infected patients; Liver International: official journal of the International Association for the Study of the Liver; Jan 2010
Last updated: Jun 05, 2023

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.⬅️

We try our best to make our Omni Calculators as precise and reliable as possible. However, this tool can never replace a professional doctor's assessment. If any health condition bothers you, consult a physician.

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.

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 - should confirm the presence of advanced fibrosis (F3-F4) in 82.1% of patients; and
  • FIB-4 < 1.45 - should exclude the presence of advanced fibrosis (F3-F4) in 94.7% of patients. (read more in article by Vallet-Pichard et al.)

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 score 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
Check out 8 similar digestive system calculators 🍽️
APRIAst alt ratioChild Pugh… 5 more
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