What is the role of lab tests in the workup of tricyclic antidepressant (TCA) toxicity in pediatric patients?

Updated: Mar 18, 2020
  • Author: Derrick Lung, MD, MPH; Chief Editor: Stephen L Thornton, MD  more...
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Answer

As in all patients with potential overdose, the following should be routinely monitored in cases of cyclic antidepressant (CA) poisoning:

  • Complete blood cell count (CBC)
  • Serum acetaminophen level
  • Electrolyte levels (with determination of anion gap)
  • Urinalysis (UA)
  • Urine or serum pregnancy test (in females of childbearing age)

Arterial blood gas (ABG) testing is also indicated. Cyclic antidepressant toxicity usually results in mixed acidosis due to respiratory depression coupled with hypotension from myocardial depression and peripheral vasodilation, thus resulting in increased lactate production. Acidemia decreases protein binding and increases plasma levels of free drug. Therefore, correction of pH is a primary target of therapy in cyclic antidepressant overdose.

In addition to serum acetaminophen levels, obtaining serum salicylate levels can also be considered. Further serum and/or urine toxicology screening for other potential co-ingestants (eg, ethanol) may be performed if indicated based on the clinical picture. Urine drug screens should not be routeinly obtained as they do not change clinical management. Serum and urine cyclic antidepressant screens are available but are notorious for false positives, including from cyclobenzaprine and diphenhydramine, and have not been shown to have clinical utility. [31]


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