Unexplained Elevations in Alanine Aminotransferase in Individuals with the Metabolic Syndrome: Results from the Third National Health and Nutrition Survey (NHANES III)

Abstract

Unexplained elevations in alanine aminotransferase (ALT) level have been suggested to signify the presence of nonalcoholic fatty liver disease (NAFLD) in adult NHANES III participants. In this study, we examined the relationship between unexplained elevations in ALT level and the metabolic syndrome and the relationship between unexplained elevations in ALT level and microalbuminuria. We examined the prevalence and predictors of unexplained elevations in ALT level in 4376 adult NHANES III participants with the metabolic syndrome. Metabolic syndrome was defined according to Adult Treatment Panel III criteria, and the presence of unexplained elevations in ALT level was defined based on the previously published criteria. Prevalence of microalbuminuria was compared between 710 individuals with unexplained elevations in ALT level and 1780 control subjects. Prevalence of unexplained elevations in ALT level in individuals with the metabolic syndrome was 7% and was significantly higher than in those without the metabolic syndrome (3.5%; OR, 2.07; 95% CI, 1.78-2.41). Younger age, male gender, higher triglycerides or serum iron levels, low levels of certain antioxidants, and insulin resistance (or diabetes) were independently associated with unexplained elevations in ALT level in the metabolic syndrome. Prevalence of microalbuminuria was not different between individuals with unexplained elevations in ALT level and their control subjects (4.8% versus 6.2%, respectively; P = 0.2). Individuals with the metabolic syndrome have a significantly higher prevalence of unexplained elevations in ALT level. Because unexplained elevations in ALT level may signify the presence of NAFLD, our data support the notion that NAFLD is part of the spectrum of the metabolic syndrome. However, no relationship was demonstrated between unexplained elevations in ALT level and microalbuminuria.