A qualitative urine immunoassay reports a category, even though the signal behind that category varies. Bang and colleagues tested the Triage TOX Drug Screen with standard materials near its cutoffs and compared results from 105 clinical urine specimens with a liquid chromatography–tandem mass spectrometry method.
At the benzodiazepine cutoff listed in the paper, 300 ng/mL of estazolam produced a positive response in 26 of 40 replicates. At 30% above that concentration, all 40 replicates were positive. Estazolam was the material used for this control. Other compounds and metabolites can trigger the antibody differently.
Seven urine samples were positive on the benzodiazepine screen and negative on the study’s comparison method. The authors noted that the methods could cover different metabolites. In a disputed sample, identify what each method targets, whether it measures conjugated metabolites, and what cutoff it applies. The screen result is a presumptive class finding. Interpretation of a named drug requires analyte-specific evidence.