Contribution of metabolic factors to alanine aminotransferase activity in persons with other causes of liver disease

Background & Aims: Nonalcoholic fatty liver disease has been defined by the presence of hepatic steatosis in the absence of other chronic liver diseases. We sought to determine whether obesity, insulin resistance, and the metabolic syndrome, which are the main risk factors for nonalcoholic fatty liver disease, are associated with similar elevations in serum alanine aminotransferase activity in persons with and those without other causes of chronic liver disease. Methods: Adult participants of the third National Health and Nutrition Examination Survey were divided into those with causes of chronic liver disease (n = 1037), defined as viral hepatitis, excessive alcohol consumption, or increased transferrin-iron saturation, and those without (n = 8004). Results: Among persons with other causes of chronic liver disease, obesity (adjusted odds ratio, 4.9; 95% confidence interval, 2.5-9.4), insulin resistance (adjusted odds ratio, 6.8; 95% confidence interval, 3.0-15.5, comparing the highest and the lowest quartile), and the metabolic syndrome (adjusted odds ratio, 3.3; 95% confidence interval, 1.4-8.0) were all strongly associated with increased alanine aminotransferase activity (>43 IU/L). Among persons without other causes of chronic liver disease, statistically similar associations were identified. Conclusions: Obesity, insulin resistance, and the metabolic syndrome are strong predictors of increased alanine aminotransferase activity in the US population, both in persons with and in persons without other causes of chronic liver disease. We hypothesize that metabolic fatty liver disease related to these conditions is the cause of the increased alanine aminotransferase activity and may be underrecognized in persons with other causes of chronic liver disease.