Tox screen
Formal Definition
A urine or serum drug toxicology panel testing for common substances of abuse and medications; urine immunoassay screens are fast but have significant false-positive and false-negative rates; serum drug levels (e.g., acetaminophen, salicylates, ethanol, lithium, digoxin) are quantitative and clinically more reliable for management decisions.
How It's Used on the Ward
"Send a tox screen" or "the tox was positive for benzos" — ordering or interpreting a urine drug screen in altered mental status or overdose presentations.
Example
""Altered 22-year-old found down by roommates: send urine tox screen, serum APAP and ASA levels, alcohol level, BMP, CBC, LFTs. Urine tox is a screening tool only — a negative result doesn't rule out overdose of non-tested substances.""
Clinical Context
Urine immunoassay screen: rapid, cheap, but unreliable. Common false positives: quinolones → opioids, proton pump inhibitors → THC, bupropion → amphetamines, rifampin → opioids. False negatives: synthetic opioids (fentanyl, methadone) do NOT show on standard opiate screen. ALWAYS send serum APAP (acetaminophen) level in any suspected intentional overdose — acetaminophen ingestion is the most underdiagnosed cause of acute liver failure, and Nomogram-guided NAC treatment is time-sensitive. Clinical toxicology panels do not test for all substances — identify the suspected agents first and order appropriately.