Evaluation of Syva EMIT Toxicological Serum Tricyclic Antidepressant Assay

Tricyclic antidepressant (TCA) overdose is a common, potentially life-threatening finding in patients seen in emergency departments. There is a need to rapidly differentiate the TCA overdose from others in the emergency unit population. The Syva EMIT Toxicological Serum Tricyclic Antidepressant Assay for serum tricyclic antidepressant levels on 87 patients being evaluated for possible TCA overdose in the emergency department of the University of Cincinnati Hospital was examined. Serum tricyclic antidepressant concentrations were also determined by high performance liquid chromatography (HPLC), and comprehensive urine drug screening was performed by several methods. The EMIT assay correctly identified all 53 negative patients whose TCA levels were less than 300 ng/mL. The remaining 34 patients had positive TCA levels greater than 300 ng/mL by EMIT; however, 22 were confirmed by HPLC. Phenothiazines and phenothiazine metabolites were present in the remaining 12 unconfirmed patients, indicating a cross reaction with this class of drugs. It was concluded that the assay is useful to exclude the presence of serious TCA ingestion when a result of less than 300 ng/mL is obtained. However, a result of greater than 300 ng/mL is not specific for TCAs only, as evidenced by the cross reactions obtained with phenothiazines.