NAFLD Fibrosis Score

The NAFLD score explained

The non-alcoholic fatty liver disease score accounts for clinical and laboratory determinations that are routinely available to determine the level of hepatic scarring.

The term NAFLD includes a series of hepatic conditions (ex. Steatosis with various degrees of inflammation) that are not associated with alcohol consumption.

The most common consequence of these conditions is the progression to end stage liver disease.

NAFLD is associated with risk factors such as type 2 diabetes mellitus, obesity, dyslipidemia or metabolic syndrome.

This is reflected in the choice of score variables that are explained in the table below:

The NAFLD formula is the following:

NAFLD Score = -1.675 + 0.037 × Age (years) + 0.094 × BMI (kg/m²) + 1.13 × IFG/diabetes (yes = 1, no = 0) + 0.99 × AST/ALT ratio – 0.013 × Platelet (×10⁹/L) – 0.66 × Albumin (g/dL).

Score interpretation

The result obtained from the formula above is placed in one of three categories:

■ Scores lower than -1.455 correlate with the absence of significant fibrosis (F0-F2 fibrosis);

■ Scores from -1.455 to 0.675 correlate with an indeterminate score;

■ Scores greater than 0.675 indicate the presence of significant fibrosis (F3-F4 fibrosis).

Following the score, patients at high risk are recommended elastography or liver biopsy whilst patients at low risk of fibrosis are to be monitored at periodic intervals.

About the study

The NAFLD score was developed by Angulo et al. in 2007 based on a study on 733 patients suffering from nonalcoholic fatty liver disease (confirmed by liver biopsy).

There were two group cohorts, one of 480 patients for score construct and one of 253 patients for validation.

The study found that age, hyperglycemia, body mass index, platelet count, albumin, and AST/ALT ratio were independent indicators of liver fibrosis in advanced stage.

A low cut-off point was established at 1.455 where advanced fibrosis could be excluded with high accuracy (negative predictive value of 93% in construct and 88% in validation group).

For the high cut-off point at 0.676, advanced fibrosis could be diagnosed with high accuracy (positive predictive value of 90% in construct and 82% in validation group).

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

As patients with NAFLD are at the highest risk of progressing to end-stage liver disease, accurate and rapid diagnosis of the stage of fibrosis they are in, is essential, as well as avoidance of invasive procedures such as liver biopsy in cases where fibrosis is unlikely.

The original score is recommended by three main authorities in the field:

■ The American Association for the Study of Liver Diseases (AASLD);

■ The American Gastroenterological Association (AGA);

■ The American College of Gastroenterology (ACG).

Hepatic fibrosis stages

Chronic and sustained attacks on the liver during hepatic inflammations lead to the creation of scarring in the form of hepatic fibrosis.

The fibrosis process is one of replacement of the damaged cells but the new cells do not maintain the hepatic functionality the original cell had.

There are five stages of hepatic fibrosis:

■ F0 and F1 are indicative of normal liver structure;

■ F2 indicates light fibrosis;

■ F3 is the stage where the fibrosis becomes severe;

■ F4 is indicative of cirrhosis with extended scar tissue.

The first stages of fibrosis may be reversed and hepatic function restored by pharmacological treatment.

Hepatic fibrosis is often accompanied by portal hypertension which leads to the creation of oesophageal varicose veins.

Other complications include ascites (abdominal liquid effusion), icterus or jaundice and hepatic encephalopathy due to the dysfunctional hepatic toxic breakdown.

Original source

Angulo P, Hui JM, Marchesini G, Bugianesi E, George J, Farrell GC, Enders F, Saksena S, Burt AD, Bida JP, Lindor K, Sanderson SO, Lenzi M, Adams LA, Kench J, Therneau TM, Day CP. The NAFLD fibrosis score: a noninvasive system that identifies liver fibrosis in patients with NAFLD. Hepatology. 2007; 45(4):846-54.

Validation

Treeprasertsuk S, Björnsson E, Enders F, Suwanwalaikorn S, Lindor KD. NAFLD fibrosis score: A prognostic predictor for mortality and liver complications among NAFLD patients. World J Gastroenterol. 2013; 19(8): 1219–1229.

Other references

1. Chalasani N, Younossi Z, Lavine JE, et al. The diagnosis and management of non-alcoholic fatty liver disease: practice guideline by the American Association for the Study of Liver Diseases, American College of Gastroenterology, and the American Gastroenterological Association. Hepatology. 2012; 55:2005-2023.

2. Dowman JK, Tomlinson JW, Newsome PN. Systematic review: the diagnosis and staging of non-alcoholic fatty liver disease and non-alcoholic steatohepatitis. Aliment Pharmacol Ther. 2011; 33(5): 525–540.

Article reviewed by Dr. Antonio Olveira