Predicting acute acetaminophen hepatotoxicity with acetaminophen-aminotransferase multiplication product and the Psi parameter

CONTEXT: Prediction of potential hepatotoxicity is important for individualizing therapy with N-acetylcysteine (NAC) in patients with acute acetaminophen overdose. Acetaminophen-aminotransferase multiplication product (APAP × AT) and the Psi Parameter (Psi) have been reported to be the predictors of acetaminophen hepatotoxicity. OBJECTIVE: To determine the validity of APAP × AT and Psi in predicting hepatotoxicity secondary to acute acetaminophen overdose. MATERIALS AND METHODS: We retrospectively reviewed acute acetaminophen overdose cases who were treated with NAC at Siriraj Hospital, Thailand during January 2004-June 2012. The patients' ages were 12 years or more. Initial acetaminophen concentration (mg/L) and aminotransferase (IU/L) were multiplied to obtain APAP × AT. Psi were derived from initial acetaminophen concentrations (mg/L) and lag time (hours) to NAC therapy. The cut-off values for APAP × AT and Psi were 1500 mg∙IU/L(2) and 5 mM∙h, respectively. Hepatotoxicity (defined as aspartate or alanine aminotransferase (ALT) greater than 1000 IU/L) was the outcome of interest. RESULTS: A total of 255 patients were included, 32 of whom developed hepatotoxicity. APAP × AT had sensitivity, specificity, and negative likelihood ratio of 90.6%, 62.8%, and 0.2, respectively. The sensitivity of Psi, specificity, and negative likelihood ratio were 96.9%, 91.5%, and 0.0, respectively. The areas under the curve of the receiver operating characteristic (ROC) curve for APAP × AT and Psi were 0.82 and 0.96, respectively, with a statistically significant difference between the two methods (p = 0.002). APAP × AT showed higher specificity (92.5%) in patients who presented 8-24 h after the overdose. DISCUSSION AND CONCLUSION: Psi and APAP × AT are valid clinical tools in predicting hepatotoxicity secondary to acute acetaminophen overdose in adults. APAP × AT is useful in predicting a low likelihood of hepatotoxicity after standard NAC therapy among late-presenting patients.