Usefulness of testing for paracetamol concentration in urine when poisoning is suspected in children

OBJECTIVES To analyze the diagnostic yield of a cut-point of 3 μg/mL for paracetamol in urine to screen for poisoning in children. MATERIAL AND METHODS Prospective case-control observational study in a pediatric intensive care unit (PICU). All enrolled patients had been admitted to the PICU. Cases were children receiving a therapeutic dose of intravenous paracetamol. Controls were not receiving paracetamol. Urine samples were collected early in the morning and 4 hours after a dose of paracetamol was received by case patients. Paracetamol concentration was measured in all samples. We compared the percentages of cases and controls who had a concentration of 3 μg/mL or more. The sensitivity, specificity, and predictive values of the cut-point were calculated. RESULTS Forty children aged between 1 month and 19 years (20 per matched group) were enrolled. Paracetamol was not detected in any of the control samples. The sensitivity of the test in early morning urine was 95% (95% CI, 85.5%-100%); specificity was 100%. The positive predictive value was 100%; the negative predictive value was 95.2% (95% CI, 86.1%-100%). Paracetamol was detected in all of the second samples collected from cases. CONCLUSION Measuring the paracetamol concentration in urine within 4 hours of dosing is useful to rule out prior intake of paracetamol and overdosing in PICU patients. Studies to validate the new cut-point of 3 μg/mL for paracetamol in urine are required with a view to possibly including it in a diagnostic protocol for suspected acute poisoning.