Purpose 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, 10 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.
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. One hundred eighteen patients (97.5%) who
reported ingesting ≥8 g had serum acetaminophen concentrations above the
‘150-line’, compared with only three patients (2.5%) who reported ingesting
<8 g (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 ≥8 g was
high (97.52%) but with low specificity (60.59%). The sensitivity of
patient-reported doses ≥10 g also was high (89.26%) with low specificity
(65.29%), whereas 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. Patient-reported ingestion of ≥8 g (as a cut-off 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.