Guide › What Is the FIB-4 Score? Calculator, Interpretation & Clinical Use

What Is the FIB-4 Score? Calculator, Interpretation & Clinical Use

1. Introduction

If you’ve been diagnosed with fatty liver disease or your doctor suspects liver problems, you may have heard about the FIB-4 score. It’s one of the most widely used tools for estimating whether your liver has developed significant scarring (fibrosis) and the best part is that it only requires information from a routine blood test.

Liver fibrosis develops silently over years or decades. By the time symptoms appear, the damage may already be advanced. This is why early detection matters so much. The FIB-4 score helps doctors identify who needs further evaluation and who can be reassured with routine monitoring.

In this article, we’ll explain what FIB-4 is, how it’s calculated, what your score means, and when you should be concerned. We’ve also included an interactive calculator so you can estimate your own score using your lab results.

2. What Is the FIB-4 Score?

The Fibrosis-4 (FIB-4) index is a simple, validated formula that estimates the likelihood of advanced liver fibrosis. It was originally developed by Sterling and colleagues in 2006 to predict significant fibrosis in patients with HIV and Hepatitis C coinfection, but it has since been validated extensively in patients with fatty liver disease (MASLD/NAFLD) and other chronic liver conditions.

The score combines four readily available pieces of information:

  • Age (in years)
  • AST (SGOT): aspartate aminotransferase, a liver enzyme
  • ALT (SGPT): alanine aminotransferase, another liver enzyme
  • Platelet count: a component of your complete blood count (CBC)

Because these values are part of routine blood work, FIB-4 can be calculated without any additional tests or costs, making it an ideal first-line screening tool.

3. The FIB-4 Formula

The FIB-4 score is calculated using this formula:

FIB-4 = (Age × AST) ÷ (Platelet count × √ALT)

Where:

  • Age is in years
  • AST (SGOT) is in U/L
  • ALT (SGPT) is in U/L
  • Platelet count is in 10⁹/L (or × 10³/µL, which is equivalent)

The formula reflects what happens biologically as the liver becomes scarred:

  • Platelet counts tend to drop as fibrosis worsens because the scarred liver produces fewer clotting factors and the spleen enlarges
  • AST may rise relative to ALT as liver cells become damaged
  • Age matters because fibrosis typically develops over many years

4. FIB-4 Calculator

Use the calculator below to estimate your FIB-4 score. You’ll need your age and three values from a recent blood test: AST (SGOT), ALT (SGPT), and platelet count.

FIB-4 Calculator

Fibrosis-4 Index for Liver Fibrosis

Formula: FIB-4 = (Age × AST) ÷ (Platelets × √ALT)
Disclaimer: This calculator is for educational purposes only and should not replace professional medical advice. Always consult a healthcare provider for diagnosis and treatment decisions.

5. How to Interpret Your FIB-4 Score

5.1 Standard Cutoffs (Age ≤65 years)

FIB-4 Score Risk Category What It Means Recommended Action
< 1.30 Low Risk Advanced fibrosis is unlikely Routine follow-up; repeat in 1-3 years
1.30 – 2.67 Indeterminate Cannot rule in or rule out fibrosis Further testing needed (FibroScan, MRE, or biopsy)
> 2.67 High Risk Advanced fibrosis is likely Hepatology referral recommended

5.2 Age-Adjusted Cutoffs (Age > 65 years)

Because age is part of the FIB-4 formula, older patients often have higher scores even without significant fibrosis. Research by McPherson and colleagues (2017) showed that using age-adjusted cutoffs improves accuracy in patients over 65:

FIB-4 Score Risk Category What It Means Recommended Action
< 2.0 Low Risk Advanced fibrosis is unlikely Routine follow-up
2.0 – 2.67 Indeterminate Cannot rule in or rule out fibrosis Further testing needed
> 2.67 High Risk Advanced fibrosis is likely Hepatology referral recommended

Important: The calculator above automatically applies the appropriate cutoffs based on the age you enter.

6. Why Is FIB-4 So Widely Used?

FIB-4 has become the go-to screening tool for liver fibrosis for several reasons:

  1. Accessibility: It uses routine lab tests available in any clinic or hospital
  2. Cost-effectiveness: No additional testing required beyond standard blood work
  3. High negative predictive value: A low FIB-4 score is excellent at ruling out advanced fibrosis (about 90% accuracy)
  4. Guideline endorsement: Recommended by major liver and diabetes organizations including AASLD, EASL, AGA, and ADA as a first-line screening tool
  5. Prognostic value: Higher FIB-4 scores correlate with increased risk of liver-related complications, cardiovascular events, and overall mortality

7. Limitations of FIB-4

While FIB-4 is useful, it’s not perfect:

  • Age dependence: May overestimate fibrosis in elderly patients (which is why age-adjusted cutoffs exist)
  • The “gray zone”: About 25-30% of patients fall into the indeterminate range and need additional testing such as liver elastography or fibroscan
  • Acute inflammation: A recent illness or flare of liver disease can temporarily elevate AST and falsely raise your FIB-4
  • Non-liver causes: Conditions that lower platelets for reasons unrelated to the liver (like blood disorders) can affect accuracy
  • Not diagnostic: FIB-4 estimates probability of fibrosis but cannot determine the exact fibrosis stage

8. What If My FIB-4 Score Is in the Indeterminate Range?

If your score falls between 1.30 and 2.67 (or 2.0 and 2.67 if you’re over 65), your doctor may recommend additional testing such as:

  • FibroScan (Transient Elastography): A quick, painless ultrasound-based test that measures liver stiffness
  • MR Elastography (MRE): An MRI-based technique that provides detailed liver stiffness mapping
  • Enhanced Liver Fibrosis (ELF) test: A blood test that measures specific fibrosis markers
  • Liver biopsy: The gold standard, but invasive; usually reserved for uncertain cases

These tests help clarify whether you truly have advanced fibrosis or whether your FIB-4 result was a false positive.

9. Tracking FIB-4 Over Time

FIB-4 can also be useful for monitoring changes in your liver health. Studies have shown that:

  • A decrease in FIB-4 over time may indicate fibrosis regression (improvement)
  • An increase in FIB-4 may suggest fibrosis progression

If you’ve made lifestyle changes like losing weight, improving your diet, or reducing alcohol intake, tracking your FIB-4 can help show whether these efforts are benefiting your liver.

10. Understanding Your Lab Values

To calculate FIB-4, you need to locate these values on your lab report:

Lab Value Also Called Normal Range Where to Find It
AST SGOT, Aspartate Aminotransferase 10-40 U/L Liver function panel or comprehensive metabolic panel
ALT SGPT, Alanine Aminotransferase 7-56 U/L Liver function panel or comprehensive metabolic panel
Platelet Count PLT, Thrombocytes 150-400 × 10⁹/L Complete blood count (CBC)

Note: Normal ranges may vary slightly between laboratories. The units for platelet count may be written as × 10⁹/L, × 10³/µL, or as thousands/µL, these are all equivalent for the FIB-4 calculation.

11. Key Takeaways

  • FIB-4 is a simple, free, and widely validated tool for estimating liver fibrosis risk
  • It uses your age and three common blood test values (AST, ALT, and platelet count)
  • A score below 1.30 (or below 2.0 if you’re over 65) is reassuring
  • A score above 2.67 warrants further evaluation by a liver specialist
  • Scores in the middle “gray zone” require additional testing to clarify
  • FIB-4 is a screening tool, not a definitive diagnosis, always discuss your results with your healthcare provider

12. References

  • Sterling RK, Lissen E, Clumeck N, et al. Development of a simple noninvasive index to predict significant fibrosis in patients with HIV/HCV coinfection. Hepatology. 2006;43(6):1317-1325. https://doi.org/10.1002/hep.21178. Original development and validation of the FIB-4 index.

  • McPherson S, Hardy T, Dufour JF, et al. Age as a Confounding Factor for the Accurate Non-Invasive Diagnosis of Advanced NAFLD Fibrosis. Am J Gastroenterol. 2017;112(5):740-751. https://doi.org/10.1038/ajg.2016.453. Addressed age-related limitations of FIB-4 and recommended adjusted cutoffs for patients over 65.

  • Angulo P, Kleiner DE, Dam-Larsen S, et al. Liver Fibrosis, but No Other Histologic Features, Is Associated With Long-term Outcomes of Patients With Nonalcoholic Fatty Liver Disease. Gastroenterology. 2015;149(2):389-397.e10. https://doi.org/10.1053/j.gastro.2015.04.043. Landmark study establishing fibrosis stage as the primary determinant of long-term outcomes in NAFLD.

  • Siddiqui MS, Vuppalanchi R, Van Natta ML, et al. Vibration-Controlled Transient Elastography to Assess Fibrosis and Steatosis in Patients With Nonalcoholic Fatty Liver Disease. Clin Gastroenterol Hepatol. 2019;17(1):156-163.e2. https://pubmed.ncbi.nlm.nih.gov/29705261/. Validated FIB-4 in a large NAFLD population.

  • Rinella ME, Lazarus JV, Ratziu V, et al. A multisociety Delphi consensus statement on new fatty liver disease nomenclature. Hepatology. 2023;78(6):1966-1986. MASLD nomenclature and diagnostic recommendations.

  • Tacke F, Horn P, Wai-Sun Wong V, et al. EASL–EASD–EASO Clinical Practice Guidelines on the management of metabolic dysfunction-associated steatotic liver disease (MASLD). J Hepatol. 2024. Current European guidelines recommending FIB-4 as first-line screening.