Interpreting tricyclic antidepressant measurements in urine in an emergency department setting: comparison of two qualitative point-of-care urine tricyclic antidepressant drug immunoassays with quantitative serum chromatographic analysis.

Patients taking tricyclic antidepressants (TCA) can experience toxicity or severe side effects. As a rapid and less technically demanding alternative to quantitative serum analysis, most laboratories offer qualitative immunoassays to assist in the evaluation of a suspected TCA overdose. However, the relationship between quantitative serum and qualitative urine levels of TCA-related compounds and their metabolites has not been comprehensively studied. Serum high-performance liquid chromatography results were compared to the qualitative urine results using the Syva Rapid Test and the Biosite Triage. Serum concentrations of amitriptyline, desipramine, doxepin, imipramine, and nortriptyline ranging from subtherapeutic to toxic triggered a positive response on both urine immunoassay devices. On the other hand, neither immunoassay uniformly detected clomipramine, even at serum levels greater than the therapeutic range. False positives due to cyclobenzaprine were more common with the Biosite assay. For virtually all positive urine TCA findings, it was not possible to determine whether the positive results corresponded to subtherapeutic, therapeutic, supratherapeutic, or toxic serum concentrations. Because urine immunoassays are the only option for many laboratories analyzing specimens for TCAs (especially in an emergency setting), clinicians must understand the limitations and interpret results in conjunction with clinical findings and/or quantitation of serum levels.