Predictive Properties of a Qualitative Urine Acetaminophen Screen in Patients with Self-Poisoning

Abstract

Objective: Screening for acetaminophen toxicity is recommended in almost all cases of self poisoning. We compared a qualitative urine acetaminophen screen to the quantitative serum acetaminophen to test the hypothesis that a negative urine acetaminophen screen would be predictive of a negative serum acetaminophen level. Methods: All adults with intentional ingestions evaluated in our Emergency Department during 1995 were retrospectively identified based on Emergency Department International Classification of Disease–9th edition codes. Laboratory data from each patient including serum and urine toxicologic assays were examined. Predictive properties of urine acetaminophen screens for serum acetaminophen were evaluated.Results: A total of 88 patients were identified who had both a serum acetaminophen and a urine acetaminophen performed. The sensitivity of the urine acetaminophen screen was 100% (95% CI 72–100%) and the specificity was 87% (95% CI 80–95%). All patients with negative urine acetaminophen screens had negative serum acetaminophen levels (negative predictive value 100%; 95% CI 96–100%). Accuracy of the urine acetaminophen screen was 89%. Conclusion: A negative urine acetaminophen screen was highly predictive of negative serum acetaminophen levels. It is possible that negative urine acetaminophen screens may obviate the need for 4-hour quantitative serum levels. Further validation in a prospective study is needed.