FIB-4 Calculator
FIB-4 uses four routine results to estimate the chance of advanced liver scarring, most often in fatty liver disease. It is a screening step that decides who needs a second test, not a diagnosis.
| Result | Interpretation |
|---|---|
| Below 1.3 | Low risk |
| 1.3 to 2.67 | Intermediate |
| 2.67 and above | High risk |
Source: 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. (doi:10.1002/hep.21178); Shah AG, Lydecker A, Murray K, et al. Comparison of noninvasive markers of fibrosis in patients with nonalcoholic fatty liver disease. Clin Gastroenterol Hepatol 2009;7(10):1104-1112. (doi:10.1016/j.cgh.2009.05.033); 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. (doi:10.1038/ajg.2016.453); Rinella ME, Neuschwander-Tetri BA, Siddiqui MS, et al. AASLD Practice Guidance on the clinical assessment and management of nonalcoholic fatty liver disease. Hepatology 2023;77(5):1797-1835. (doi:10.1097/HEP.0000000000000323)
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FIB-4 formula
FIB-4 = (age × AST) ÷ (platelets × √ALT)
Age in years, AST and ALT in U/L, and platelets in 10⁹/L (the same number as 10³/µL on most US lab reports).
Worked example
Age 55, AST 40, ALT 36, platelets 200: (55 × 40) ÷ (200 × 6) = 1.83, which is intermediate risk.
What your FIB-4 means
These cut-offs come from the AASLD 2023 guidance for fatty liver disease:
| FIB-4 | Risk of advanced scarring | Usual next step |
|---|---|---|
| Below 1.3 | Low | Stay with primary care; repeat every 1 to 3 years if you have metabolic risk factors |
| 1.3 up to 2.67 | Intermediate | A second test: liver stiffness scan (elastography) or ELF blood test |
| 2.67 or above | High | Consider referral to a liver specialist |
Two age adjustments matter:
- Age 65 or older: use 2.0, not 1.3, as the low-risk cut-off. FIB-4 rises with age alone, so the standard cut-off flags too many older adults.
- Under 35: FIB-4 is not reliable at this age and should not be used to rule scarring in or out.
The guidance also says FIB-4 should not be used in someone who is acutely ill.
Hepatitis C uses different numbers
FIB-4 was first developed in people with HIV and hepatitis C, using cut-offs of 1.45 and 3.25 for a different scale of liver scarring. Those numbers are not interchangeable with the fatty liver cut-offs above, which is why this calculator reports only the fatty liver bands.
FAQs
What is a normal FIB-4 score?
Below 1.3 is low risk for advanced liver scarring, or below 2.0 if you are 65 or older. FIB-4 has no “normal” as such; it sorts people by risk.
What should I do if my FIB-4 is between 1.3 and 2.67?
Guidelines recommend a second test rather than a conclusion: usually a liver stiffness scan (elastography) or an ELF blood test, or referral to someone who can arrange one.
Is FIB-4 accurate?
It is best at ruling scarring out. In the fatty liver study that set the cut-offs, 90% of people scoring 1.3 or below did not have advanced scarring, which is why it is used as the first step. A high score is followed up by a liver specialist.
Does FIB-4 work for young people?
No. It performs poorly under age 35 and should not be used to decide anything at that age.