Diagnostic Approach to Nonalcoholic Fatty Liver Disease

Introduction to NAFLD Diagnosis

The American Association for the Study of Liver Diseases recommends that an AST:ALT ratio <1 is characteristic of nonalcoholic fatty liver disease (NAFLD), though this pattern is not diagnostic on its own and does not exclude other causes of liver disease 1, 2
The European Association for the Study of the Liver states that in NAFLD, the AST:ALT ratio is typically <1, meaning ALT is elevated more than AST 1, 2, 3

The American College of Gastroenterology notes that an AST:ALT ratio ≥2 strongly suggests alcoholic liver disease (70% of cases have ratio >2) 4
The National Institute on Alcohol Abuse and Alcoholism states that an AST:ALT ratio >3 is highly specific for alcoholic etiology 4

The NAFLD liver fat score (NLFS) specifically incorporates the AST/ALT ratio as a diagnostic parameter, with lower ratios supporting NAFLD diagnosis 2
The American Association for the Study of Liver Diseases recommends calculating the FIB-4 score to assess fibrosis risk (score >2.67 indicates high risk for advanced fibrosis) 3

The American Heart Association suggests evaluating for obesity, type 2 diabetes, hypertension, and dyslipidemia—the core components of metabolic syndrome that drive NAFLD 1, 5
The American Diabetes Association states that in patients with type 2 diabetes, 42-65% have hepatic steatosis 5

The American Association for the Study of Liver Diseases recommends considering hepatology referral if ALT remains elevated ≥6 months without identified cause 3
The European Association for the Study of the Liver suggests considering hepatology referral if ALT increases to >5× upper limit of normal 3
The American College of Gastroenterology states that evidence of synthetic dysfunction (elevated INR, hypoalbuminemia, thrombocytopenia) is an indication for hepatology referral 1
The National Institute of Diabetes and Digestive and Kidney Diseases recommends considering hepatology referral if FIB-4 score >2.67 or transient elastography >12.0 kPa suggesting advanced fibrosis 3