Measuring plasma paracetamol concentrations in all patients with drug overdoses; development of a clinical decision rule and clinicians willingness to use it.

OBJECTIVES: The study proposed a clinical decision rule: In patients who have taken a deliberate overdose, but deny taking paracetamol or paracetamol containing compounds, who have a GCS of 15, understand English well, and have not taken excessive alcohol, there is no need to take blood for paracetamol estimation.
METHODS: 307 consecutive emergency department patients were followed up, and the history of their overdose was correlated to blood paracetamol concentrations. In addition, clinicians were asked what level of confidence they required from such a clinical decision rule before they would use it.
RESULTS: 152 admitted paracetamol and 155 denied it. Of the 155 that denied it, 13 had concentrations detected in the blood, but needed no treatment with antidote. Eighty three per cent of clinicians require a false negative rate of less than 1%.
CONCLUSIONS: Using this decision rule, only 46 of 307 patients would not have required paracetamol concentrations to be measured. To show a negative rate of less than 1% a sample size of 20,000 patients would be needed. BOTTOM LINE: All patients who allege taking an overdose need paracetamol concentrations checking.