Accuracy of body mass index in detecting an elevated alanine aminotransferase level in adolescents

Aim: We evaluated the accuracy of body mass index (BMI) in detecting an elevated alanine aminotransferase (ALT) level in adolescents, taking into account the effects of gender, age, ethanol intake, hepatitis B virus (HBV) and hepatitis C virus (HCV) infections, and drug consumption. Subjects: A representative sample of 454 adolescents (11-17 years) from two cities in northern Italy was studied (the Dionysos Study). Methods: z-BMI was calculated as the z-score of BMI using national growth charts. Logistic regression was used to quantify the contribution of the variables of interest to an elevated ALT (> 30 UL-1). Odds ratios (OR) and 95% confidence intervals (95% CI) were calculated, and areas under receiver-operator characteristic curves (AUC) were used to evaluate accuracy. Results: An elevated ALT was detected in 21 adolescents (4.6%). Among the studied variables, only male gender (OR 6.7, 95% CI 2.0-23.2) and z-BMI (OR=2.1, 95% Cl 1.4-3.2) were significant predictors of elevated ALT. The accuracy of the prediction was 0.69 (95% CI 0.59-0.79) for gender and 0.71 (95% CI 0.59-0.81) for z-BMI. By combining gender and z-BMI, the accuracy rose to 0.80 (95% CI 0.71-0.89). Conclusion: BMI is a good predictor of elevated ALT in Italian adolescents and gender adds to the accuracy of the prediction.