Fatty Liver Index (FLI)

FLI explained

The diagnosis of fatty liver is usually done through ultrasonography, computed tomography (CT), or magnetic resonance imaging (MRI) of the abdomen.

These can detect excess fat in the liver but in a lot of cases, liver biopsy is also necessary to determine whether inflammation or fibrosis are present and to confirm the diagnosis.

Ultrasound is the first-line tool to detect liver steatosis but it's costly, operator-dependant, not widely available and only detects steatosis if present in more than 20-30% of hepatocytes. Therefore, there is an increasing interest to perform simple, accurate, and less expensive scores.

There are several steatosis biomarkers (models that help diagnosis) available, with different sensitivities and specificities, most of which that have been validated independently. There are also studies that compare and test them with different results.

In the original study by Bedogni et al. data from 216 subjects with and 280 without suspected liver disease was analysed. Fatty liver was diagnosed through ultrasonography and patients were asked to keep a 7-day record of their alcohol intake. 13 variables of interest were initially identified as potential predictors of the disease.

Four predictors were included in the final algorithm:

■ BMI – measured in kg per sqm. This is the surrogate measure for body adiposity (from patient weight and height).

■ Waist circumference – there is a higher risk of non-alcoholic fatty liver disease complications in non-obese patients with a large waist circumference.

■ Triglycerides – high levels of serum triglycerides are associated with FL, pancreatitis and kidney disease.

■ Serum GGT (gamma-glutamyl transpeptidase) – this enzyme is found in liver tissue and can be used as marker for liver function.

The FLI formula that calculates the likelihood of fatty liver disease is:

FLI = (e^0.953*log_e ^{(triglycerides) + 0.139*BMI + 0.718*log}_e ^{(ggt) + 0.053*waist circumference - 15.745}) / (1 + e^0.953*log_e ^{(triglycerides) + 0.139*BMI + 0.718*log}_e ^{(ggt) + 0.053*waist circumference - 15.745}) x 100

The following table introduces the parameters that are used to create the formula:

Result interpretation

The FLI scores vary between 1 and 100 and the original study set up the negative and positive likelihood cut-off points at 30 and 60:

■ FLI scores below 30 indicate that FL should be ruled out (with a negative likelihood ratio of up to 0.2);

■ FLI scores between 30 and below 60 remain inconclusive;

■ FLI scores of 60 and above indicate that FL is present (with a positive likelihood ratio starting from 4.3).

FLI’s positive predictive value (PPV) at scores greater than 60 is of 99% whilst the negative predictive value (NPV) is of 15%.

The following table contains the statistical values for the extended fatty liver index intervals:

The FLI showed a 0.84 (95%CI 0.81–0.87) accuracy in detecting FL in the original study cohort, which has prompted it being proposed as surrogate marker of nonalcoholic fatty liver disease (NAFLD).

Please note that the FLI score has been validated in a single-liver disease population and that patients with HCV, HBV etc. have been excluded.

The score is missing EASL endorsement, because of it being reliant on waist circumference, a measurement not recorded in standard medical reports, as compared to the Hepatic Steatosis Index (HSI), that is EASL endorsed.

Hepatic steatosis biomarkers

These are other examples of tools that help clinicians with diagnosis of non-alcoholic fatty liver disease:

■ ALD/NAFLD Index (ANI) – which distinguishes alcoholic liver disease from NAFLD;

■ TyG Index – for both insulin resistance and risk of NAFLD;

■ Non-Alcoholic Fatty Liver Disease - Liver Fat Score (NAFLD-LFS).

Original source

Bedogni G, Bellentani S, Miglioli L, Masutti F, Passalacqua M, Castiglione A, Tiribelli C. The Fatty Liver Index: a simple and accurate predictor of hepatic steatosis in the general population. BMC Gastroenterol. 2006; 6:33.

Other references

1. Fedchuk L, Nascimbeni F, Pais R, Charlotte F, Housset C, Ratziu V; LIDO Study Group. Performance and limitations of steatosis biomarkers in patients with nonalcoholic fatty liver disease. Aliment Pharmacol Ther. 2014; 40(10):1209-22.

2. Kahl S, Straßburger K, Nowotny B, Livingstone R, Klüppelholz B, Keßel K, Hwang JH, Giani G, Hoffmann B, Pacini G, Gastaldelli A, Roden M. Comparison of liver fat indices for the diagnosis of hepatic steatosis and insulin resistance. PLoS One. 2014; 9(4):e94059.

3. Motamed N, Sohrabi M, Ajdarkosh H, Hemmasi G, Maadi M, Sima F et al. Fatty liver index vs waist circumference for predicting non-alcoholic fatty liver disease. World J Gastroenterol. 2016; 22(10): 3023–3030.

Article reviewed by Dr. Antonio Olveira