Let’s compare them!
What each index is designed to do:
Fatty Liver Index (FLI)
Best for: Detecting hepatic steatosis (fatty liver)
- What it estimates: Presence of liver fat
- Inputs: BMI, waist circumference, triglycerides, GGT
- Primary use: Screening for MASLD / NAFLD in the general population
- Output: Score 0–100
- <30: Fatty liver unlikely
- ≥60: Fatty liver likely
Strengths
- Good for early disease detection
- Useful in population screening and primary care
- Non-invasive and inexpensive
Limitations
- Does not assess fibrosis
- Less useful once disease is established
- Influenced by obesity and metabolic factors
FIB-4 Index
Best for: Detecting advanced liver fibrosis
- What it estimates: Risk of significant / advanced fibrosis
- Inputs: Age, AST, ALT, platelet count
- Primary use: Risk stratification and referral decisions
- Output (typical cutoffs):
- <1.3: Low risk of advanced fibrosis
- >2.67: High risk of advanced fibrosis
Strengths
- Excellent negative predictive value for advanced fibrosis
- Strong evidence base across liver diseases
- Endorsed by AASLD, EASL, ADA
Limitations
- Poor for detecting steatosis
- Less accurate in younger patients and the elderly
- Can be affected by acute inflammation
If the goal is–
| Clinical goal | Better index |
|---|---|
| Identify fatty liver (steatosis) | FLI |
| Identify advanced fibrosis | FIB-4 |
| Decide who needs hepatology referral | FIB-4 |
| Population-level screening | FLI → FIB-4 |
| Long-term outcome prediction | FIB-4 |
At LiverRight, we see them as complementary–
Typical pathway:
- FLI → identifies who likely has fatty liver
- FIB-4 → identifies who is at risk for advanced fibrosis
- Elastography / specialist care → for high-risk patients
This stepwise approach reduces unnecessary referrals while catching patients who matter most.
Bottom line
- FLI = “Is there fat?”
- FIB-4 = “Is there dangerous scarring?”
FLI first, FIB-4 second is often the most efficient and evidence-based strategy.
Consider another view, in the December 2025 recent article titled “Poor Sensitivity of the Fatty Liver Index Among Lean Individuals” in the American Journal of GASTROENTEROLOGY–
📌 Summary
The study likely found that:
- The Fatty Liver Index (FLI) has low sensitivity in detecting hepatic steatosis (fatty liver) in certain populations when compared with a reference standard such as imaging (e.g., ultrasound).
- “Poor sensitivity” means that a substantial number of people who actually have fatty liver are missed by the FLI — in other words, the test falsely categorizes them as not having fatty liver. This undermines its usefulness as a screening tool in some clinical settings.
- The article’s message is consistent with broader evidence showing that while FLI can stratify risk, it does not reliably identify all patients with fatty liver, especially in early or mild cases or in populations with different body composition or metabolic profiles. Iris
📌 Why FLI Shows Poor Sensitivity in Some Studies
Other research has shown that:
- FLI may achieve moderate accuracy overall, but its ability to rule in or rule out steatosis can vary widely depending on population characteristics (age, ethnicity, BMI, etc.). Iris
- Meta-analyses show FLI sensitivity can range from ~44% to ~81% depending on the cutoff used and reference standard, meaning a significant proportion of true cases may be missed. Iris
- This limitation is more pronounced in cohorts with lower degrees of liver fat, or where BMI and metabolic factors differ from the population in which FLI was originally derived. Iris
📌 What “Poor Sensitivity” Means Clinically
- A test with poor sensitivity fails to detect many true cases → not good for screening on its own.
- If you use FLI alone, many individuals with actual fatty liver might be classified as “low probability” and miss follow-up imaging or care.
- That’s why clinicians often use FLI as part of a stepwise approach with imaging or other biomarkers.