The FIB-4 score is a quick, evidence-based way to estimate the risk of advanced liver fibrosis using common lab values and age. Use the calculator below to get an instant estimate, then review the interpretation guide to understand what your result may mean.
FIB-4 Score Calculator
What Is the FIB-4 Score?
FIB-4 (Fibrosis-4 Index) is a non-invasive scoring tool used to estimate the probability of significant liver scarring (fibrosis), especially in people with metabolic dysfunction-associated steatotic liver disease (MASLD), viral hepatitis, or other chronic liver conditions. It helps clinicians decide who may need additional testing such as elastography or specialist referral.
How the FIB-4 Calculator Works
This calculator combines four inputs: age, AST, ALT, and platelet count. These are routine clinical values, which makes FIB-4 practical in primary care and specialist settings.
- Age: Age in years at time of testing.
- AST: Aspartate aminotransferase (U/L).
- ALT: Alanine aminotransferase (U/L).
- Platelets: Platelet count, usually expressed as 109/L.
Formula: FIB-4 = (Age × AST) / (Platelet Count × √ALT)
Interpreting Your Result
Adults Under 65
- Below 1.3: Lower likelihood of advanced fibrosis.
- 1.3 to 2.67: Indeterminate zone; follow-up testing may be needed.
- Above 2.67: Higher likelihood of advanced fibrosis; further evaluation is recommended.
Adults 65 and Older
- Below 2.0: Lower likelihood of advanced fibrosis in older adults.
- 2.0 to 2.67: Indeterminate zone; additional testing may clarify risk.
- Above 2.67: Higher likelihood of advanced fibrosis.
Why Clinicians Use FIB-4
- It is quick, low-cost, and uses routine laboratory data.
- It helps prioritize patients for further non-invasive tests.
- It can reduce unnecessary referrals in low-risk groups.
- It supports population-level risk stratification in primary care.
Example Calculation
Suppose a 52-year-old patient has AST 58 U/L, ALT 72 U/L, and platelets 180 (109/L):
FIB-4 = (52 × 58) / (180 × √72) = 3016 / (180 × 8.49) = 3016 / 1528.2 = 1.97
For someone under age 65, 1.97 falls in the indeterminate range and may prompt additional evaluation.
Important Limitations
- FIB-4 is a screening/risk tool, not a stand-alone diagnosis.
- Acute illness, active inflammation, alcohol use, and temporary lab fluctuations can affect results.
- Age influences score, so interpretation differs in older adults.
- Low platelets may occur for reasons unrelated to liver fibrosis.
What to Do After You Calculate
- Save your score and input values.
- Discuss trends over time, not just one result, with your clinician.
- If your score is indeterminate or high, ask whether elastography or hepatology referral is appropriate.
- Address modifiable risks: weight, blood sugar, lipids, alcohol intake, and physical activity.
Frequently Asked Questions
Is this calculator a diagnosis?
No. It estimates risk and supports next-step decisions. Diagnosis requires clinical assessment and sometimes imaging or biopsy.
Can I use non-fasting labs?
Usually yes for FIB-4 itself, but your clinician may still request fasting labs depending on your broader metabolic evaluation.
How often should I recalculate?
Frequency depends on your risk profile and care plan. Many patients repeat fibrosis risk testing periodically as advised by their provider.