Objectives: The present study examines the relationship between the dose of acetaminophen reported to have been ingested by patients and the occurrence of serum acetaminophen levels above the ‘possible toxicity’ line in patients presenting at the hospital after acetaminophen overdose. The prognostic value of patient-reported dosage cut-offs of 8 g, 10 g and 12 g was determined.

Methods: This retrospective cohort study included patients admitted to the emergency department or hospital within 24 hours of acetaminophen ingestion. Serum acetaminophen concentrations were considered to be the gold standard, and specificity, sensitivity, and positive/negative predictive values were calculated from the reported ingested dose, to predict toxicity using the Rumack–Matthew nomogram (i.e. the ‘possible toxicity’ treatment line) and standard equations.[1,2]

Results: Of 305 patients identified, 291 met the study inclusion criteria, and 121 (41.6%) had serum acetaminophen concentrations above the ‘possible toxicity’ treatment line. The range of patient-reported acetaminophen ingested was 1–75 g, with 185 patients (63.6%) reporting ‡8 g. 118 patients (97.5%) who reported ingesting ‡8 g had serum acetaminophen concentrations above the ‘150-line’, compared with only 3 patients (2.5%) who reported ingesting < 8g (p< 0.001). The positive predictive value of a patient-reported dose ‡8 g for predicting serum acetaminophen concentrations above the ‘possible toxicity’ treatment line was 63.78%, with a negative predictive value of 97.17%. The sensitivity of patient-reported doses ‡8g was high (97.52%), but with low specificity (60.59%). The sensitivity of patient-reported doses ‡10 g was also high (89.26%) with low specificity (65.29%), while the sensitivity of ‡12 g dose was low (61.16%) with high specificity (86.47%).

Conclusions: Patient-reported doses of acetaminophen are good risk indicators for acetaminophen overdose patients in Malaysia. Patientreported ingestion of ‡8 g (as a cutoff dose) had a higher sensitivity than ‡10 g or ‡12 g. The results of this study have important implications for toxicity risk evaluations in areas with poor serum acetaminophen assay availability.

References

1. Rumack BH, Matthew H. Acetaminophen poisoning and toxicity. Pediatrics 1975; 55: 871-6

2. Rumack BH, Peterson RC, Koch GG, et al. Acetaminophen overdose. 662 cases with evaluation of oral acetylcysteine treatment. Arch Intern Med 1981; 141: 380-5