Explainer
FIB-4, explained
A four-number formula that helps doctors decide who needs a closer look at their liver. Here is its history, its cutoffs and its blind spots.
What FIB-4 measures
FIB-4 estimates the chance of advanced fibrosis, meaning heavy scarring of the liver, from age, two liver enzymes (AST and ALT) and the platelet count (Sterling 2006). It does not measure liver fat. Fatty liver disease is common and often silent; the danger is when it leads to scarring (NIDDK).
What is a normal FIB-4 score?
There is no single normal value. FIB-4 is read against two cutoffs that sort adults with fatty liver disease, or its risk factors, into three groups (Shah 2009) (AASLD 2023):
| FIB-4 result | What it suggests | Usual next step |
|---|---|---|
| Below 1.30 | Advanced scarring is unlikely | Recheck later if risk factors remain |
| 1.30 to 2.67 | Indeterminate | A second test, such as elastography or an ELF blood test |
| Above 2.67 | Advanced scarring is more likely | Referral to a liver specialist |
At age 65 or older, a low cutoff of 2.0 instead of 1.30 gives fewer false alarms (McPherson 2017). A result is a reason for a conversation with a doctor, not a diagnosis.
Where it came from
FIB-4 was created in 2006 from 832 people with both HIV and hepatitis C, using liver biopsy as the reference (Sterling 2006). In that study, a value under 1.45 ruled out advanced fibrosis with a negative predictive value of 90%, and a value over 3.25 had a specificity of 97% (Sterling 2006).
In 2009, a US study of 541 adults with fatty liver disease from the NASH Clinical Research Network found FIB-4 outperformed several other non-invasive markers and proposed cutoffs of 1.30 and 2.67 for that group (Shah 2009). These are the cutoffs most fatty liver guidance uses today, including the AASLD 2023 guidance (AASLD 2023).
Age changes the picture
Because age is in the formula, FIB-4 climbs with age even when the liver is fine. A 2017 study of 634 people with fatty liver disease found that at 65 or older, the usual low cutoff gave a specificity of only 35% (McPherson 2017). Using 2.0 as the low cutoff at 65 or older raised specificity to 70% (McPherson 2017). At 35 or younger, FIB-4 barely beat chance (AUROC 0.60) (McPherson 2017).
What doctors usually do next
The AASLD guidance uses FIB-4 as a first step for people with fatty liver disease or its risk factors. A result of 1.30 or more usually leads to a second test, such as liver stiffness measurement by elastography or an ELF blood test, and higher-risk results to a liver specialist (AASLD 2023).
When FIB-4 can mislead
- Acute liver injury (for example hepatitis or heavy recent drinking) can raise AST and ALT for reasons other than scarring.
- Conditions that lower platelets for other reasons can raise FIB-4.
- It was not designed for children.
Sources
- 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.org/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.org/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.org/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.org/10.1097/HEP.0000000000000323
- National Institute of Diabetes and Digestive and Kidney Diseases (NIH). Nonalcoholic Fatty Liver Disease (NAFLD) and NASH. www.niddk.nih.gov/health-information/liver-disease/nafld-nash
Written and maintained by the uncovermyrisk.com editorial team. We do not have a medical reviewer; every claim links to its primary source above. Last reviewed: 2026-10-26. Spotted an error? See About.