Is Serum Alanine Aminotransferase (ALT) Elevation in Obese Children and Adolescents Just Non-Alcoholic Fatty Liver Disease (NAFLD)?

Abstract

Purpose: Unexplained ALT elevation is present in up to 23% of obese children. ALT elevation in insulin-resistant obese patients is used as a surrogate for diagnosis of NAFLD. Serum ALT level is considered abnormal by some above 40 U/L or above the upper limit of normal in the reference laboratory. The prevalence of other liver disease such as autoimmune hepatitis (AIH) is not known in this population. We hypothesize that serum ALT elevation in obese children and adolescent warrants comprehensive evaluation for liver disease other than NAFLD. Methods: Retrospective chart review of all patients referred for evaluation and management of obesity. Clinical data (BMI, age, gender) are recorded. Serum ALT level available from a screening comprehensive metabolic profile was recorded using a cut off of 48 U/L (our laboratory's upper limit of normal). Results: A total of 506 charts were available for review, 92 (18%) patients did not complete the laboratory evaluations, 42 (8%) patients had a serum ALT drawn at outside laboratories and therefore were excluded because of differing reference ranges. The remaining 372 (74%) patients had a serum ALT level recorded, 84 (23%) greater than 48 U/L. In this population of elevated serum ALT, 37 (43%) are female and 42 (50%) are White. The mean BMI (±SD) is 39 ± 11 kilos/m2. The mean age (±SD) is 14 ± 4 years old. Four (5%) patients have liver disease other than NAFLD. One patient (an African-American adolescent female) has mild α1 antitrypsin deficiency (PiMZ). Three (4%) patients (2 African-American adolescent females and 1 adolescent White male) have Smooth Muscle antibody positive and Anti-Nuclear antibody positive compatible with Autoimmune Hepatitis Type 1. Two of the patients with AIH had ALT greater than 1.5 times upper limit of normal, but one did not. If a threshold of serum ALT level greater than 40 U/L is used, then the prevalence of patients with abnormal ALT is 158 (42%), with no differences in demographics or BMI. Conclusion: In our population of obese children and adolescents, the prevalence of ALT elevation above laboratory cut off (>48 U/L) was comparable to a previous study. A threshold of 40 U/L would indicate a higher, previously unreported, prevalence of 42%. Autoimmune hepatitis prevalence was high (4%). Therefore, we suggest that in obese children and adolescents where the prevalence of abnormal serum ALT is high, values of serum ALT above the upper limit of laboratory reference warrant a comprehensive evaluation for liver disease as it cannot be assumed to represent only NAFLD.