What are the diagnostic criteria for Non-Alcoholic Fatty Liver Disease (NAFLD)?

From the Guidelines

The diagnosis of Non-Alcoholic Fatty Liver Disease (NAFLD) requires evidence of hepatic steatosis either by imaging or histology, absence of significant alcohol consumption, and exclusion of other causes of liver disease, as defined by the presence of steatosis in >5% of hepatocytes according to histological analysis or by a proton density fat fraction >5.6% assessed by proton magnetic resonance spectroscopy (1 H-MRS) or quantitative fat/water selective magnetic resonance imaging (MRI) 1. To diagnose NAFLD, the following criteria should be met:

• Hepatic steatosis by imaging or histology
• Absence of significant alcohol consumption, defined as >30 g/day for men and >20 g/day for women 1
• Exclusion of other causes of liver disease, such as hepatitis C, medications, parenteral nutrition, Wilson’s disease, and severe malnutrition 1 The diagnostic workup for NAFLD typically begins with:
• Abnormal liver function tests showing elevated ALT and AST
• Ultrasound imaging to detect steatosis when fat content exceeds 20-30%
• More sensitive imaging options, such as CT scan, MRI, or MR spectroscopy
• Laboratory tests, including complete liver function tests, lipid profile, fasting glucose, and HbA1c to evaluate metabolic risk factors
• Testing for viral hepatitis, autoimmune markers, and iron studies to exclude other liver diseases Liver biopsy remains the gold standard for diagnosis, but is typically reserved for cases where the diagnosis is unclear or to assess disease severity and stage fibrosis 1. Non-invasive fibrosis assessment tools, such as FIB-4, NAFLD Fibrosis Score, or Enhanced Liver Fibrosis test, can help identify patients at higher risk of advanced fibrosis 1. The diagnosis of NAFLD should be considered in patients with metabolic syndrome features, including obesity, type 2 diabetes, hypertension, and dyslipidemia, as these conditions frequently coexist with NAFLD 1.

From the Research

Diagnosis Criteria for NAFLD

The diagnosis of Nonalcoholic Fatty Liver Disease (NAFLD) involves several criteria, including:

• Hepatic steatosis detected either on histology or imaging without a secondary cause of abnormal hepatic fat accumulation 2
• The presence of characteristic sonographic findings on bedside ultrasound, such as bright hepatic echoes, increased hepatorenal echogenicity, vascular blurring of portal or hepatic vein, and subcutaneous tissue thickness 2
• A hepatic fat content of 5% or greater, as defined by nonalcoholic fatty liver (NAFL) or nonalcoholic steatohepatitis (NASH) 3

Imaging Modalities for NAFLD Diagnosis

Various imaging modalities can be used for the diagnosis and quantified measurement of hepatic fat content, including:

• Ultrasound-based methods, which can provide characteristic sonographic findings for NAFLD 2
• Magnetic Resonance Imaging (MRI)-based methods, such as proton density fat-fraction (PDFF), T2 *, and T1 mapping, along with MR elastography 4
• Computed Tomography (CT) scans, which can detect fat infiltration in the liver 5

Limitations of Imaging Modalities

While imaging modalities can be useful for diagnosing NAFLD, they have several limitations, including:

• Liver biopsy is currently the most accurate method for evaluating hepatic steatosis, but it has several limitations, such as invasiveness, sampling error, and high cost 6
• Ultrasound cannot replace liver biopsy in staging the degree of fibrosis 2
• Non-invasive quantification of hepatic steatosis by imaging has been challenging, but recent MRI techniques show great promise in the detection and quantification of liver fat 5