Impact of toxicology screens in the diagnosis of a suspected overdose: salicylates, tricyclic antidepressants, and benzodiazepines.

A retrospective review of 150 cases determined the contribution of salicylate assays, tricyclic antidepressant (TCA) screens, and benzodiazepine screens to the diagnosis of overdose patients. Seventy percent of salicylate assays and 42% of TCA screens were ordered when there was no history of ingestion of clinical indication of overdose with these agents. In 12% of the cases benzodiazepine screens did not provide useful information. A positive history of salicylate ingestion, tinnitus and hyperventilation were the best predictive indicators of salicylate ingestion. The best predictors of TCA toxicity were a positive history of ingestion, a decreased level of consciousness, and a prolonged QRS interval. The combination of a positive history of ingestion and a decreased level of consciousness was a sensitive indicator of benzodiazepine toxicity. The annual cost of screens/assays which did not contribute to diagnosis was estimated to be $4649. Based on this study, a thorough history and clinical assessment of the overdose patient takes precedence over analytical screens in determining the drug(s) involved.