Measuring plasma salicylate concentrations in all patients with drug overdose or altered consciousness: is it necessary?

BACKGROUND Salicylate self poisoning is potentially fatal. Plasma salicylate concentrations can be used to guide management when taken in the context of clinical features of toxicity and acid base status. Previous studies in the USA and Hong Kong have shown that routine measurement of plasma salicylate concentrations in all overdose patients is inappropriate, but there have been no previous studies in the UK. METHODS A retrospective case note study from 1 February 2001 to 31 January 2002 was undertaken at the emergency department of St. Thomas' Hospital, London. Records were reviewed and information on demographic data, history, details of salicylate overdose, and documentation of clinical features of salicylate toxicity recorded. RESULTS In total, 722 patient episodes were identified, of which 596 case notes were available and appropriate for inclusion in this study. Plasma salicylate concentrations (range 15-428 mg/l) were detectable in 50 patients (three notes not available), of whom 38 had given a positive history. The history of salicylate poisoning had a sensitivity of 81% (95% confidence interval (CI) 67 to 91%) and the predictive value of a negative history of salicylate ingestion in not detecting salicylate concentrations was 98% (95% CI 97 to 99%). Insufficient information on clinical features of salicylate toxicity was recorded in 569 patients (including 35 patients who had a history of salicylate ingestion). CONCLUSION History of salicylate ingestion has a high sensitivity and negative predictive value with respect to the detection of plasma salicylate concentrations. However, current practice indicates that insufficient information is obtained from patients about the clinical features of toxicity. Routine measurement of plasma salicylate concentrations is not required unless there is (a) a positive history of ingestion of salicylates or (b) a reduced level of consciousness or other reason limiting the validity of the history obtained, together with clinical features consistent with salicylate poisoning.