A laboratory may be able to distinguish a drug signal from background at a concentration too low to report as a reliable number. A study of four benzodiazepines in vitreous humor illustrates that distinction.
The researchers used liquid–liquid extraction and high-performance liquid chromatography with a diode-array detector. They tested flurazepam, lorazepam, alprazolam and diazepam and applied the method to 21 authentic vitreous samples. They reported a detection limit of 30 ng/mL and a quantitation limit of 100 ng/mL for the four analytes. The paper also reported a calibration curve extending down to 30 ng/mL.
The low end of the calibration curve and the validated quantitation limit answer different questions. For this method, a signal between those reported limits may support detection, while a numerical concentration in that interval lacks the study’s stated support for quantitation. In a case review, ask for the reporting laboratory’s own matrix-specific limits and how it qualified the result.
Study of four benzodiazepines in vitreous humor (full text) · DOI