nondetectable

Nondetectable refers to a result or condition that cannot be detected by a given measurement or analytical method. It indicates that the concentration or level of a target substance is below the method’s detection limit rather than proven to be absent. The exact meaning of nondetectable depends on the sensitivity of the instrument, the assay, or the testing protocol being used.

In measurement and testing, nondetectable results are common when the concentration is too low to distinguish from background noise. Analytical systems specify a detection limit or limit of detection (LOD) and, in many cases, a limit of quantitation (LOQ). Results may be reported as nondetectable, below the LOD, or below the LOQ, with the latter sometimes yielding a quantitative estimate that is uncertain.

In medicine, nondetectable is frequently used to describe the absence of measurable levels of a substance, such as a viral load or drug metabolite, relative to an assay’s sensitivity. A nondetectable result often suggests a favorable response to treatment but does not guarantee absence of the substance, since lower concentrations may exist below the assay’s threshold.

In environmental science and toxicology, nondetectable results indicate that a contaminant was not observed above the method’s detection limit in a sample. Handling nondetects in data analysis requires careful consideration, as simple substitution with a fixed value can bias results; more advanced approaches treat nondetects as censored data.

Overall, nondetectable conveys a practical limit of measurement rather than an absolute zero, with the interpretation dependent on the testing method and context.