How can I differentiate between alcoholic and non-alcoholic liver disease based on liver function test results?

Distinguishing alcoholic liver disease (ALD) from non-alcoholic fatty liver disease (NAFLD) based solely on liver function tests (LFTs) is challenging because both conditions can present with elevated liver enzymes; however, certain patterns and clinical context can aid differentiation. In ALD, the aspartate aminotransferase (AST) to alanine aminotransferase (ALT) ratio is typically greater than 2, reflecting mitochondrial damage from alcohol toxicity, whereas in NAFLD, ALT is usually higher than AST or the ratio is less than 1, consistent with hepatocellular injury from metabolic causes ¹,³. Both conditions may show elevated gamma-glutamyl transferase (GGT), but GGT elevation is more pronounced in ALD due to alcohol induction of microsomal enzymes ¹,³. Alkaline phosphatase (ALP) and bilirubin may be elevated in advanced disease or cirrhosis in both ALD and NAFLD but are not specific for differentiation ¹,². Importantly, LFTs alone cannot definitively distinguish ALD from NAFLD; a thorough alcohol history is essential to rule out alcohol misuse, as recommended by NICE guidelines ¹,³. Additional non-invasive tests such as transient elastography or enhanced liver fibrosis (ELF) testing can assess fibrosis severity but do not differentiate etiology ¹,². Liver biopsy remains the gold standard for diagnosis when clinical and biochemical findings are inconclusive, especially in suspected ALD with severe hepatitis ³. Recent literature supports these biochemical patterns but emphasizes the overlap and the need for comprehensive clinical assessment including metabolic risk factors for NAFLD and alcohol consumption history (Mulhall et al., 2002; Karim et al., 2015). Thus, while LFT patterns provide clues, differentiation relies on integrating LFT results with clinical history and further diagnostic evaluation ¹,³ (Mulhall et al., 2002; Karim et al., 2015).