A urine drug screen answers a question about its tested analytes and specimen. A 2017 prospective study of ICU admissions illustrates how a negative urine result can coexist with other evidence supporting intoxication.
The investigators enrolled 65 adults admitted from an emergency department to intensive care during a six-month period. Inclusion could be supported by clinical presentation, history, or toxicology findings. Patients could enter before screening results were available. People admitted for another reason were excluded even if they had a positive screen.
The paper reported 55 patients with a positive urine or serum toxicology screen, while 23 had a negative urine screen. Serum ethanol was detected in 23 patients. The combined urine-or-serum outcome and the urine-only outcome therefore measured different things. The study also described targeted liquid chromatography–tandem mass spectrometry testing when synthetic-cannabinoid intoxication was suspected.
A negative result needs the test menu, detection limits, specimen, and collection time for interpretation. This selected ICU cohort provides limited information about how often a negative screen excludes poisoning in an unselected emergency population. The study’s enrollment process itself allowed clinical evidence to support inclusion. In an individual review, separate the reason intoxication was suspected from the substances actually detected and the evidence that links an exposure to the presenting illness. Those distinctions explain the apparent discrepancy without treating different tests as interchangeable.
Read the full scientific paper. DOI 10.1080/20009666.2017.1356189.