A 23-month-old patient with a seizure disorder presented to the emergency department after a suspected unintentional ingestion of his seizure medication. He had significant central nervous system depression and seizure-like movements. Although at the time of presentation it was known that the patient ingested his antiseizure medication, the name of the medication was not known. Also, it was not clear if the patient coingested any other drug. Broad-spectrum urine drug screening by immunoassay and GC-MS that includes presumptive screening of >200 drugs and toxins was ordered. Additionally, volatile screening for ethanol, methanol, acetone, and isopropanol was ordered. Carbamazepine testing that is available on a stat basis on the Vitros 5600 Chemistry Analyzer was also requested. Urine drug screening by GC-MS (GC-7890, MS-5975; Agilent) showed the presence of carbamazepine and oxcarbazepine. Carbamazepine concentration measured by immunoassay on the Vitros 5600 Chemistry Analyzer (Ortho-Clinical Diagnostics) was 7.9 μg/mL (therapeutic range, 4-12 μg/mL). Unless there was a coingestion of another drug,

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