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

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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 (1H-MRS).

A cross-sectional study was conducted in 129 healthy subjects. Liver triglyceride content was quantified by 1H-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 23 IU/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 23 IU/L identified 94% of individuals with NAFLD in the present series, using 3-T 1H-MRS for liver triglyceride quantification.

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