Explain 'non-detect' and 'below the limit of quantitation' in sample results.

• A. Non-detect means below the limit of detection; below the limit of quantitation means detected but not quantified; both affect risk interpretation and may require resampling
• B. Non-detect means the sample is negative; LOQ is the same as LOD
• C. Non-detect means below LOD; below LOQ means detected and quantified
• D. Non-detect means concentration is exactly zero; LOQ is not applicable

Answer: (A)

The key idea is distinguishing between the ability to detect something and the ability to quantify it. The limit of detection is the smallest amount that can be reliably distinguished from background noise. If the analyte’s concentration is below that level, the result is a non-detect. The limit of quantitation is higher; it’s the smallest amount that can be measured with acceptable precision and accuracy. If an analyte is present but too low to quantify, the result is detected but below the limit of quantitation. In practice, you might see a result described as detected but not quantified, or as non-detect, depending on where the true concentration lies relative to these limits. Importantly, a non-detect does not prove zero concentration; it simply means the amount is below what the method can reliably detect. Both situations influence risk interpretation and may lead to resampling or confirmatory testing to obtain a numeric value. The statements that mix up LOD and LOQ or claim that non-detect equals zero or negative are not accurate.