Breath alcohol analyzer mistakes methanol poisoning for alcohol intoxication.

Breath alcohol analyzers are used to detect ethanol in motorists and others suspected of public intoxication. One concern is their ability to detect interfering substances that may falsely increase the ethanol reading. A 47-year-old-man was found in a public park, acting intoxicated. A breath analyzer test (Intoxilyzer 5000EN) measured 0.288 g/210 L breath ethanol, without an interferent noted. In the emergency department, the patient admitted to drinking HEET Gas-Line antifreeze, which contains 99% methanol. Two to three hours after ingestion, serum and urine toxicology screen results were negative for ethanol and multiple other substances. His serum methanol concentration was 589 mg/dL, serum osmolality 503 mOsm/kg, osmolar gap 193 mOsm/kg, and anion gap 17 mmol/L. The patient was treated with intravenous ethanol, fomepizole, and hemodialysis without complication. This is a unique clinical case of a breath alcohol analyzer reporting methanol as ethanol. Intoxilyzer devices have been shown to indicate some substances (acetone) as interferents in humans but not methanol. Increased serum concentrations of methanol can be reported as ethanol by a commonly used breath alcohol analyzer, which can result in a delayed diagnosis or misdiagnosis and subsequent methanol toxicity if antidotal treatment is not administered in a timely manner.

Quetiapine cross-reactivity with plasma tricyclic antidepressant immunoassays.

BACKGROUND: Toxicology screens obtained on patients who have overdosed on drugs frequently include tricyclic antidepressants (TCAs) as part of the evaluation. Quetiapine is an antipsychotic agent with structural similarity to the TCAs. OBJECTIVE: To determine whether quetiapine may cross-react with plasma TCA immunoassays in vitro using commonly available autoanalyzers. METHODS: Quetiapine stock solution was added to 9 separate samples of pooled drug-free human plasma to produce concentrations ranging from 1 to 640 ng/mL that were verified by gas chromatography. No quetiapine metabolites were present. Each spiked plasma sample was tested in a blinded fashion using the Abbott Tricyclic Antidepressant TDx Assay on the TDxFLx autoanalyzer in 2 separate laboratories, the Syva Emit tox Serum Tricyclic Antidepressant Assay on the AU400 autoanalyzer and the S TAD Serum Tricyclic Antidepressant Screen on the ACA-Star 300 autoanalyzer. The TDx assay is quantitative, while Emit and S TAD are qualitative screening assays with a threshold of 300 ng/mL for TCA positivity. The outcome of interest was a positive TCA result. RESULTS: The quantitative assay showed concentration-related TCA cross-reactivity beginning at quetiapine concentrations of 5 ng/mL. The 640-ng/mL spiked sample produced TCA results of 379 and 385 ng/mL in labs 1 and 2, respectively. The qualitative assays were screened as TCA positive at quetiapine concentrations of 160 and 320 ng/mL for the S TAD and Emit assays, respectively. CONCLUSIONS: Quetiapine cross-reacts with quantitative and qualitative plasma TCA immunoassays in a concentration-dependent fashion. Therapeutic use or overdose of quetiapine may result in a false-positive TCA immunoassay result.