To the Editor Dr Greer and colleagues attempted to standardize the diagnosis of BD/DNC within and across countries.1 However, drug ingestion complicates the diagnosis of BD/DNC. The authors recognized that brain death mimics exist and that some of these mimics are reversible. However, we have several concerns.
First, toxicology screens are unreliable indicators of ingestion. Commonly available urine drug screens test for opiates but not opioids. These screens do not routinely detect fentanyl, a synthetic opioid, which contaminates much of the US heroin supply. Benzodiazepines are equally problematic. Urine drug screens for benzodiazepines usually detect oxazepam or nordiazepam, metabolites that are not universal within the drug class, resulting in a failure to detect lorazepam or clonazepam. In addition to these false negatives, false positives are possible. For example, recent ingestion of labetalol can cause a positive screening result for amphetamines on immunoassay.2 Moreover, even if the presence of a drug is confirmed with more specific quantitative testing, such as gas chromatography/mass spectroscopy, the concentration implies nothing about the drug’s toxicity for a particular patient. For a patient with a long history of alcohol use disorder, an ethanol concentration of 400 mg/dL would contribute to their clinical presentation very differently than for someone who is naive to ethanol. In addition, many drugs that mimic BD/DNC, such as baclofen,3 are not part of routine drug screens. Put simply, a positive drug screen does not confirm toxicity and a negative drug screen does not exclude it.