What is the FIB-4 index?

FIB-4 (Fibrosis-4) is a non-invasive liver fibrosis score calculated from age, AST, ALT, and platelet count. It estimates the likelihood of significant liver fibrosis (METAVIR F2-F4) in chronic liver diseases including NAFLD/MASLD, hepatitis C, and hepatitis B, without requiring a liver biopsy.

How is FIB-4 calculated?

FIB-4 = (Age [years] × AST [U/L]) ÷ (Platelet count [×10⁹/L] × √ALT [U/L]). All four values are available from a routine blood count and liver function panel. The formula was derived from HIV/HCV co-infected patients and later validated broadly in NAFLD and viral hepatitis.

What is the normal range for FIB-4?

Standard cutoffs: FIB-4 2.67 = high fibrosis risk (likely F3-F4), warrants hepatology referral. In patients >65 years, age-adjusted lower cutoff of 2.0 is recommended to reduce false positives.

How does FIB-4 compare to APRI?

Both are non-invasive fibrosis tests. FIB-4 consistently shows higher AUROC than APRI for advanced fibrosis across NAFLD, HCV, and HBV cohorts (~0.85 vs ~0.78). FIB-4 requires four variables (age, AST, ALT, platelets) vs APRI's two (AST, platelets). The 2023 AASLD/AGA MASLD pathway recommends FIB-4 as the preferred first-line test over APRI.

What is FIB-4's role in NAFLD/MASLD management?

The 2023 AASLD/AGA Multi-Society Clinical Care Pathway recommends FIB-4 as the primary non-invasive test for fibrosis staging in all MASLD patients. FIB-4 2.67: refer urgently to hepatology for comprehensive evaluation and HCC surveillance consideration.

What is liver fibrosis and why does it matter?

Liver fibrosis is the accumulation of scar tissue in the liver as a response to chronic injury (fatty liver, hepatitis, alcohol, etc.). Fibrosis is staged by METAVIR F0 (none) to F4 (cirrhosis). Advanced fibrosis (F3-F4) is associated with portal hypertension, liver failure, and hepatocellular carcinoma risk. Early detection allows intervention before irreversible cirrhosis develops.

What is FibroScan and when is it used after FIB-4?

FibroScan (vibration-controlled transient elastography, VCTE) is a non-invasive device that measures liver stiffness as a surrogate for fibrosis. In the 2023 AASLD/AGA MASLD pathway, FibroScan is the recommended second-line test when FIB-4 falls in the indeterminate zone (1.30–2.67). Liver stiffness 35.

When does FIB-4 indicate cirrhosis?

FIB-4 >2.67 has approximately 80% positive predictive value for advanced fibrosis (F3-F4). While FIB-4 cannot diagnose cirrhosis definitively, a high FIB-4 combined with clinical signs (thrombocytopenia, splenomegaly, portal hypertension on imaging) makes cirrhosis highly likely. Confirmation with FibroScan (LSM ≥15 kPa) or liver biopsy may be required before initiating HCC surveillance or esophageal variceal screening.

How is FIB-4 used in hepatitis C?

FIB-4 was originally developed in HIV/HCV co-infected patients (Sterling et al., Hepatology 2006) and performs well in HCV monoinfection. FIB-4 3.25 has high PPV. Pre-treatment fibrosis staging with FIB-4 guides the decision to prioritize treatment access in resource-limited settings.

What are the main limitations of FIB-4?

Key limitations: (1) Age effect — elderly patients (>65) systematically have higher FIB-4, requiring age-adjusted cutoffs. (2) Thrombocytopenia from non-hepatic causes (ITP, hypersplenism) inflates FIB-4 artificially. (3) Acute hepatitis flares transiently elevate AST and FIB-4. (4) A large proportion of patients fall in the indeterminate zone requiring additional testing. (5) Cannot diagnose specific etiology of fibrosis.

How does FIB-4 change over time in monitoring?

Serial annual FIB-4 measurements are recommended in MASLD patients. A rising FIB-4 indicates fibrosis progression and should prompt intensified evaluation. A falling FIB-4 (e.g., after 10% weight loss, bariatric surgery, or effective MASLD therapy) suggests fibrosis regression. Crossing from one risk zone to another is clinically significant — particularly crossing from low to indeterminate or indeterminate to high risk.

How does FIB-4 perform in elderly patients?

Because age is in the FIB-4 numerator, patients >65 years have systematically inflated FIB-4 values independent of fibrosis severity. Studies show that using standard FIB-4 cutoffs in the elderly increases false-positive rates significantly. Age-adjusted guidance (McPherson et al. 2017) recommends using 2.0 as the upper threshold for the indeterminate zone in patients >65, reducing unnecessary FibroScan referrals in low-risk elderly patients.

Online Medical Tools — FIB-4

Printed on 9/2/2026

For informational purposes only. This is not medical advice.

Gastroenterology

FIB-4

FIB-4 is a non-invasive fibrosis risk score widely used in chronic liver disease triage, including NAFLD and viral hepatitis pathways. It helps identify low-risk patients versus those needing elastography or specialist evaluation.

Formula: FIB-4 = (Age x AST) / (Platelets x sqrt(ALT)).

Age

years

AST

U/L

ALT

U/L

Platelet Count

x10^9/L

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How It Works

Collect four laboratory and clinical variables

FIB-4 requires four inputs available from a standard complete blood count and liver function panel: patient age (years), AST (U/L), ALT (U/L), and platelet count (×10⁹/L, also reported as k/µL). These are routinely available at any outpatient or inpatient encounter. No special imaging or invasive testing is needed for the initial FIB-4 calculation.

Calculate FIB-4 using the validated formula

FIB-4 = (Age × AST) / (Platelet count × √ALT). The numerator multiplies age and AST; the denominator multiplies platelet count by the square root of ALT. For example, a 55-year-old with AST 55 U/L, ALT 48 U/L, and platelets 210 ×10⁹/L: FIB-4 = (55 × 55) / (210 × √48) = 3025 / (210 × 6.93) = 3025 / 1455 = 2.08. Most EHR systems and hepatology order sets now calculate FIB-4 automatically.

Interpret and act on the FIB-4 result using the 2023 AASLD/AGA pathway

Three zones guide clinical action: FIB-4 <1.30 = low fibrosis risk (F0-F1 by METAVIR); reassure patient and reassess annually. FIB-4 1.30–2.67 = indeterminate zone — refer for vibration-controlled transient elastography (VCTE/FibroScan) or other validated second-line test (ELF score, liver biopsy in selected cases). FIB-4 >2.67 = high fibrosis risk (likely F3-F4/cirrhosis); refer promptly to hepatology for comprehensive evaluation, portal hypertension assessment, and HCC surveillance consideration. In patients >65 years, age-adjusted thresholds (lower cutoff ≥2.0) reduce false positives.

Who Uses the FIB-4

NAFLD/MASLD Fibrosis Staging in Primary Care

Primary care physicians and internists

The 2023 AASLD/AGA Clinical Care Pathway recommends FIB-4 as the first-line non-invasive test for fibrosis assessment in all patients with NAFLD/MASLD. Calculate at diagnosis and annually to monitor progression or response to lifestyle intervention.

Hepatitis C Fibrosis Assessment

Infectious disease physicians and hepatologists

FIB-4 is validated in HCV-infected patients (including HIV/HCV co-infection where it was originally developed) for pre-treatment fibrosis staging and monitoring. FIB-4 >3.25 in HCV identifies patients likely to have cirrhosis needing additional monitoring.

Hepatitis B Fibrosis Monitoring

Hepatologists and gastroenterologists

Serial FIB-4 measurements in chronic HBV infection help track fibrosis progression during antiviral therapy. Rising FIB-4 over time despite viral suppression may signal inadequate fibrosis regression or concurrent NAFLD.

Metabolic Syndrome Liver Evaluation

Endocrinologists and metabolic medicine physicians

In patients with type 2 diabetes, obesity, or metabolic syndrome, FIB-4 identifies those at advanced fibrosis risk who need hepatology referral vs those who can be safely monitored in primary care with dietary counseling.

Replacing Liver Biopsy in Initial Assessment

Hepatologists

For patients with FIB-4 <1.30 (low risk) or FIB-4 >2.67 (high risk), the clinical decision is clear and biopsy can often be avoided. The indeterminate zone (1.30–2.67) is where FibroScan or second-line NITs inform the need for biopsy.

Annual Monitoring in Fatty Liver Patients

All clinicians managing chronic liver disease

FIB-4 should be recalculated annually in patients with known NAFLD/MASLD. A rising FIB-4 that crosses from low to indeterminate or indeterminate to high risk zones indicates accelerating fibrosis and should prompt immediate hepatology referral.

Pro Tips

FIB-4 is the endorsed first-line test by AASLD and AGA for NAFLD/MASLD

The 2023 AASLD/AGA Multi-Society Clinical Care Pathway (Rinella et al., Gastroenterology 2023) explicitly recommends FIB-4 as the primary non-invasive tool for fibrosis assessment in MASLD, ahead of APRI and NAFLD Fibrosis Score due to its superior accuracy and simplicity.

FIB-4 <1.3 has >90% negative predictive value for significant fibrosis

In large validation cohorts, FIB-4 <1.30 has a negative predictive value exceeding 90% for METAVIR F2-F4 fibrosis. This makes it highly useful for ruling out significant fibrosis and safely avoiding elastography in the majority of low-risk NAFLD patients in primary care.

FIB-4 >2.67 has approximately 80% positive predictive value for advanced fibrosis

While not as high as the NPV, FIB-4 >2.67 identifies patients very likely to have F3-F4 disease. These patients should be referred to hepatology for FibroScan confirmation, HCC surveillance enrollment (if cirrhotic), esophageal variceal screening, and consideration of liver-directed therapy.

Indeterminate zone (1.30–2.67) requires second-line testing

Approximately 20–40% of NAFLD patients fall in the indeterminate FIB-4 zone. Per AASLD/AGA 2023, these patients should proceed to vibration-controlled transient elastography (FibroScan/VCTE), the ELF score, or enhanced liver fibrosis test. Do not simply repeat FIB-4 in 3 months — it is unlikely to reclassify the patient without significant clinical change.

Age >65 years inflates FIB-4 — use age-adjusted cutoffs

Because age is in the FIB-4 numerator, elderly patients (>60–65 years) systematically have higher FIB-4 values. McPherson et al. (J Hepatol 2017) proposed using a lower cutoff of 2.0 (instead of 2.67) as the upper threshold for the indeterminate zone in patients >65 years, reducing false-positive advanced fibrosis classifications in the elderly.

Acute hepatitis flares transiently elevate FIB-4

Acute AST or ALT spikes from any cause (viral hepatitis flares, drug-induced liver injury, ischemic hepatitis) elevate FIB-4 substantially. Do not calculate FIB-4 during an acute hepatocellular injury episode. Wait until transaminases return to baseline (or chronic level) before using FIB-4 for fibrosis staging.

Thrombocytopenia from any cause elevates FIB-4 falsely

FIB-4 divides by platelet count — any cause of low platelets (immune thrombocytopenia, hypersplenism, drug-induced thrombocytopenia, bone marrow suppression) will mathematically inflate FIB-4 independent of liver fibrosis. Always review the etiology of a low platelet count before attributing elevated FIB-4 to liver disease.

FIB-4 is superior to APRI for advanced fibrosis staging

Multiple meta-analyses comparing FIB-4 and APRI across NAFLD, HCV, and HBV cohorts show FIB-4 has higher AUROC for advanced fibrosis (approximately 0.85 vs 0.78 for APRI). AASLD/AGA 2023 recommends FIB-4 as the preferred initial test over APRI in MASLD management pathways.

Platelet decline itself is a sign of portal hypertension and cirrhosis

In chronic liver disease, progressive thrombocytopenia from hypersplenism (portal hypertension-induced splenic sequestration) drives FIB-4 upward — both directly (lower denominator) and as a signal of evolving cirrhosis. A patient whose platelet count is falling over serial measurements even while transaminases are stable may be developing clinically significant portal hypertension.

FIB-4 can be used for monitoring response to weight loss treatment in MASLD

Body weight loss of 7–10% (or more) improves steatosis and inflammation and can improve NIT scores including FIB-4 over 12–24 months. Serial annual FIB-4 measurement provides objective tracking of fibrosis trajectory in patients undergoing lifestyle intervention, GLP-1 agonist therapy, or bariatric surgery evaluation.

Common Questions About Your Results

Per 2023 AASLD/AGA pathway, indeterminate FIB-4 (1.30–2.67) should prompt second-line testing: vibration-controlled transient elastography (FibroScan/VCTE) is the preferred next step. An LSM (liver stiffness measurement) <8 kPa generally rules out significant fibrosis; ≥12–15 kPa suggests cirrhosis. Do not simply repeat FIB-4 without clinical change — it is unlikely to reclassify out of the indeterminate zone.

Evidence-Based Methodology

FIB-4 was developed by Sterling et al. (Hepatology 2006) in 847 HIV/HCV co-infected patients and subsequently validated in NAFLD by Shah et al. (Clin Gastroenterol Hepatol 2009). AUROC for advanced fibrosis (≥F3) is approximately 0.85 in NAFLD and 0.87 in HCV. The 2023 AASLD/AGA Multi-Society Clinical Practice Guideline on MASLD (Rinella et al., Gastroenterology 2023) recommends FIB-4 as the primary non-invasive test for fibrosis assessment. Age-adjusted thresholds for patients >65 years were proposed by McPherson et al. (J Hepatol 2017).

Clinical Content Trust

Last reviewed:: April 21, 2026
Guideline version:: General evidence framework v2026.04
Source set version:: Primary-source set v1

How to Interpret Your Result

Lower FIB-4 values suggest lower probability of advanced fibrosis, while higher values indicate greater risk and need for further evaluation.

When to Use This Tool

Use FIB-4 for non-invasive fibrosis risk stratification in chronic liver disease pathways and primary care-to-hepatology triage.

Limitations

FIB-4 can be confounded by acute transaminase elevations, age effects, and non-hepatic platelet abnormalities. It should not replace definitive fibrosis assessment when clinically indicated.

Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health.

Changelog

April 21, 2026 · trust-baseline
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