The Fatty Liver Index, usually shortened to FLI, estimates the probability that fat has built up inside your liver, using four ordinary inputs: body mass index, waist circumference, fasting triglycerides and GGT. Two of those come from a scale and a tape measure; the other two come from a blood draw, so this is not a measurement you can finish at home. Nothing beyond a routine lab is needed, though: no ultrasound appointment, no elastography, no specialist referral.
It was published in 2006 from an Italian general-population study as a way of deciding who is worth imaging, and that is still the job it does well.
What you need
- Your height and weight, for body mass index.
- Your waist circumference in centimeters, measured on bare skin with a flexible, non-stretch tape.
- Your fasting triglycerides, from a standard lipid panel drawn after roughly 9 to 12 hours without food.
- Your GGT (gamma-glutamyl transferase), from a liver panel. This is the input most often missing: many checkup packages include ALT and AST but not GGT, so ask for it by name.
Nothing else enters the score. Age is not used, and unlike several related indices there is no separate male and female version. The original equation expects triglycerides in mg/dL and GGT in U/L, so a triglyceride value reported in mmol/L has to be converted first.
How the measurement works
Take the waist standing, at the end of a normal breath out, with the tape midway between the lowest rib and the top of the hip bone, snug and level all the way around.
The four numbers then go into a single logistic equation, each with a fixed weight, and the output is compressed onto a 0 to 100 scale that reads as a likelihood rather than an amount of fat. All four push the same way: a higher BMI, a larger waist, higher triglycerides and higher GGT each raise the score, and the two body measures carry most of the weight, which matters when you come to the limits. Rather than working the coefficients by hand, put your four values into the Fatty Liver Index (FLI) and let it do the arithmetic. If your panel came back without GGT, the Hepatic Steatosis Index (HSI) asks the same question from ALT, AST and BMI instead.
How to read the result
| FLI score | Standard reading |
|---|---|
| Below 30 | Fatty liver is unlikely. This end of the scale is built to rule steatosis out. |
| 30 to 59 | The gray zone. The score cannot settle the question either way. |
| 60 and above | Fatty liver is likely. Imaging and a clinical assessment are the sensible next step. |
The two cut-offs were chosen for different jobs, one to rule steatosis out and one to rule it in, which is why the middle band is left undecided rather than being labeled “mild”. In the derivation cohort the score separated people with and without ultrasound-detected fatty liver with an area under the ROC curve of about 0.84. That is good enough to triage, and not good enough to conclude.
What it does not tell you
FLI does not measure liver fat. It estimates how likely an ultrasound would be to find it, and ultrasound itself misses milder steatosis. A score below 30 therefore means “probably not enough fat for a scan to see”, not “no fat”.
It also says nothing about the two things that determine outcome: inflammation and scarring. A high FLI cannot separate simple steatosis from steatohepatitis, and it does not stage fibrosis at all – that is a separate calculation from different inputs, which is what the FIB-4 Fibrosis Index exists for.
Nor does it identify a cause. GGT rises with regular alcohol intake, with enzyme-inducing medications, and with any obstruction of bile flow, so the score can climb for reasons unrelated to metabolic fatty liver. And because BMI and waist dominate the equation, FLI under-detects fatty liver in lean people and flags heavy people whose livers are clean.
Finally, it was derived in Italian adults; reported performance and the best local cut-offs vary across populations, and the index is not established for children, adolescents or pregnancy. Treat any result above the lower cut-off as a reason to see a clinician, not as a verdict.
Related reading
Disclaimer. This article is for information only and does not replace medical advice. Talk to a qualified clinician before changing anything about your health.