GPT and hemochromatosis type 1: The prevalence of ALT elevation unexplained by viral hepatitis, hemochromatosis, or alcoholism (i.e., suspected NAFLD) was 10.6% in NHANES 2003–2004, which was nearly double the prevalence (5.4%) reported by a study of NHANES 1988–1994 adult participants that used similar exclusion criteria and a similar ALT reference range (Clark et al. 2003).