Acetaminophen psi nomogram: A sensitive and specific clinical tool to predict hepatotoxicity secondary to acute acetaminophen overdose

Abstract

Background: Acetaminophen Psi Parameter (APP) is a composite of acetaminophen (paracetamol) level and lag time before N-acetylcysteine (NAC) therapy. The APP is a significant predictor of hepatotoxicity secondary to acute acetaminophen overdose. Acetaminophen Psi Nomogram (APN) was invented as a graphic analog of the APP for use in predicting individual patient's risk of hepatotoxicity. Clinical accuracy of the APN has never been validated. Objective: The authors are reporting the validity of APN in predicting hepatotoxicity secondary to acute acetaminophen overdose at Siriraj Hospital. Material and Method: This present study is a retrospective review of medical records of patients with acute acetaminophen overdose at Siriraj Hospital between January 2004 and June 2009. Each case was classified by APN into an appropriate risk group. The outcome of interest was hepatotoxicity. The validity of the APN is reported as sensitivity and specificity. Secondary outcomes include serum acetaminophen concentrations, delay to NAC therapy, and APP for each APN's risk group. Results: One hundred and sixty-one patients were enrolled. Higher APN risk classifications are associated with a trend towards higher acetaminophen levels, longer delayed to NAC initiation, and larger APP. Twenty five patients (15.5%) developed hepatotoxicity. The number of patients who were above the APN's risk lines, 1% and 50% were 88 (54.7%) and 17 (10.6%), respectively, with corresponding sensitivities of 100.0% (95% CI 86.6, 100.0) and 40.0% (95% CI 21.2, 61.3). APN's risk lines 50% had specificity of 94.9% (95% CI 89.7, 97.9). Conclusion: Acetaminophen Psi Nomogram is a sensitive and specific tool for prediction of hepatotoxicity secondary to acute acetaminophen overdose. By application of the APN, a significant proportion of patients may not require either further follow-up after the completion of NAC therapy or prolongation of NAC therapy. Patients in high APN's risk ranges may be treated and monitored more intensively with confidence.