What blood tests are indicative of Nonalcoholic Fatty Liver Disease (NAFLD)?

From the Guidelines

Blood tests that can indicate Nonalcoholic Fatty Liver Disease (NAFLD) include elevated liver enzymes, particularly alanine aminotransferase (ALT) and aspartate aminotransferase (AST), as well as specific NAFLD fibrosis markers like the NAFLD Fibrosis Score and FIB-4 index. These enzymes are typically mildly to moderately elevated in NAFLD, with ALT often higher than AST 1. Other relevant tests include gamma-glutamyl transferase (GGT), which may be elevated, and markers of metabolic syndrome such as fasting glucose, lipid panel (showing high triglycerides and low HDL cholesterol), and insulin levels indicating insulin resistance.

The NAFLD Fibrosis Score and FIB-4 index are non-patented tests that can help assess disease severity, with the NAFLD Fibrosis Score based on six readily available variables (age, BMI, hyperglycemia, platelet count, albumin) and the FIB-4 index based on the combination of age, AST, ALT, and platelet count 1. These scores use two cut-offs to rule-out or rule-in advanced fibrosis, with the NAFLD Fibrosis Score having a cut-off of -1.455 for ruling out advanced fibrosis and the FIB-4 index having a cut-off of 1.3 1.

It's essential to note that normal liver enzymes don't rule out NAFLD, as up to 80% of patients may have normal ALT/AST levels. These blood tests should be interpreted alongside imaging studies like ultrasound, FibroScan, or MRI, which can directly visualize liver fat content and assess fibrosis. Blood tests help monitor disease progression and treatment response but aren't definitive for diagnosis without additional clinical evaluation.

Some key points to consider when interpreting blood tests for NAFLD include:

• Elevated liver enzymes, particularly ALT and AST, suggest liver inflammation and damage
• Specific NAFLD fibrosis markers like the NAFLD Fibrosis Score and FIB-4 index can help assess disease severity
• Normal liver enzymes don't rule out NAFLD
• Imaging studies like ultrasound, FibroScan, or MRI can directly visualize liver fat content and assess fibrosis
• Blood tests should be interpreted alongside clinical evaluation and imaging studies to diagnose and monitor NAFLD.

From the Research

Blood Tests for Nonalcoholic Fatty Liver Disease (NAFLD)

The following blood tests are indicative of Nonalcoholic Fatty Liver Disease (NAFLD):

• Serum alanine aminotransferase (ALT) levels 2, 3
• γ-glutamyltransferase (GGT) levels 2
• Enhanced liver fibrosis (ELF) test 4
• FibroMeterV2G 4
• FibroMeterV3G 4
• NAFLD fibrosis score (NFS) 4, 5
• Fibrosis-4 index (FIB-4) 4, 5
• Fatty liver index (FLI) 5

Diagnostic Accuracy of Blood Tests

The diagnostic accuracy of these blood tests varies, with some studies suggesting that:

• ELF score, FibroMeterV2G, FibroMeterV3G, and liver stiffness measurement (LSM) have superior diagnostic accuracy for noninvasive diagnosis of fibrosis stage in NAFLD compared to FIB-4 and NFS 4
• Serum ALT and GGT concentrations within the reference ranges are associated with the incidence of NAFLD and metabolic syndrome in a dose-dependent manner 2
• Metabolic factors, rather than ALT levels, are associated with histological severity of NAFLD 3

Limitations of Blood Tests

It is essential to note that:

• Liver biopsy remains the gold standard for making a definitive diagnosis of NAFLD and nonalcoholic steatohepatitis (NASH) 6, 5
• Blood tests should be used in conjunction with other diagnostic tools, such as ultrasound and medical history, to confirm the diagnosis of NAFLD 5