There is concordance between the indications for treatment of paracetamol deliberate self-poisoning based on plasma and saliva paracetamol levels. Saliva paracetamol levels are typically higher than plasma levels. Further studies involving larger numbers of patients, comparing plasma and saliva paracetamol levels in patients with potentially toxic plasma paracetamol concentrations, would be useful in determining the potential clinical value of this method.

Background: In the laboratory evaluation of suspected paracetamol poisoning, a non-invasive sample type that avoids venepuncture would be an attractive alternative to plasma, particularly in the paediatric setting. Salivary paracetamol measurement has not previously been evaluated in the published medical literature in the setting of deliberate self-poisoning (DSP). Methods: In-house validation experiments (recovery, stability and lower limit-of-detection) were performed on pooled saliva samples using a Roche Acetaminophen assay on a Roche/Hitachi 917 analyser. A clinical study of comparison of paired saliva and plasma samples was also conducted involving adult patients presenting with DSP of paracetamol, the results of which were published previously. Results: The validation experiments using pooled saliva samples showed: (i) mean recovery ( paracetamol concentration 37.5-525 mg/L) 100.01% (+0.02 SD); (ii) precision of repeated assay over 24-h period CV ,4%; (iii) lower limit-of-detection 0.9 mg/L. The clinical study of 21 patients with mean plasma paracetamol concentration of 48 mg/L (range 0 -130) and mean saliva concentration 62 mg/L (range 0 -183) showed good correlation between saliva and plasma concentrations (r 2 ¼ 0.91).