Define LOD and LOQ in the context of drug testing?

• A. LOD is the highest concentration that can be detected; LOQ is the lowest concentration that can be detected.
• B. LOD is the lowest concentration that can be reliably distinguished from background; LOQ is the lowest concentration that can be quantified with acceptable precision and accuracy.
• C. LOD is the minimum detectable signal; LOQ is the maximum detectable signal.
• D. LOD and LOQ refer to the solvent preparation rather than the sample.

Answer: (B)

In drug testing, two sensitivity thresholds describe how well an assay performs. The limit of detection is the lowest amount of drug that can be reliably told apart from the background noise, meaning you can say the drug is present but you may not know its exact amount with confidence. The limit of quantification is the lowest amount that can be measured with acceptable precision and accuracy, so the reported concentration is dependable.

In practice, LOD and LOQ are set using criteria such as signal-to-noise ratios or the variability seen in blank samples and calibration data. A typical approach is that LOD corresponds to a smaller signal above background, while LOQ requires a stronger signal to ensure reliable quantitation. This distinction matters because a result can be detectable but not quantifiable, and reporting standards often treat detections below LOQ differently than those above it.