Diagnostic accuracy of serum alanine aminotransferase as biomarker for nonalcoholic fatty liver disease and insulin resistance in healthy subjects, using 3T MR spectroscopy

Recognition of the close relationship of nonalcoholic fatty liver disease (NAFLD) with diabetes mellitus 2, obesity, metabolic syndrome, and cardiovascular disease has stimulated growing interest in NAFLD as a public health problem. Serum alanine aminotransferase (ALT) has been proposed as a marker of NAFLD, but levels are within the range currently considered "normal" in a large proportion of NAFLD subjects. The aim of the study was to determine the diagnostic accuracy of serum ALT for identifying individuals with NAFLD, using 3-Tesla (T) magnetic resonance spectroscopy (H-1-MRS). A cross-sectional study was conducted in 129 healthy subjects. Liver triglyceride content was quantified by H-1-MRS. NAFLD was defined as liver triglyceride content greater than 5.56%. Liver triglyceride content was > 5.56% in 79 participants (NAFLD) and lower in the remaining 50 (normal). Serum ALT levels correlated positively with liver triglyceride content (r=0.58, P<.001), Homeostatic Model Assessment for Insulin Resistance (r=0.32, P<.01), and fasting insulin (r=0.31, P<.01), and inversely correlated with adiponectin (r=0.35, P<.01) and high-density lipoprotein cholesterol (r=0.32, P<.01). Regression analysis showed that serum ALT was the best predictor of NAFLD (P<.01). Optimal serum ALT cut-off to predict NAFLD was 23IU/L (area under receiver-operating characteristic curve: 0.93; sensitivity: 0.94; specificity: 0.72). This study shows that serum ALT is a sensitive and accurate biomarker of NAFLD if the "normal" ALT value is revised and established at a lower level. An ALT threshold of 23IU/L identified 94% of individuals with NAFLD in the present series, using 3-T H-1-MRS for liver triglyceride quantification.