Limit of Quantitation (LOQ)
Definition
The lowest concentration at which the assay can produce a quantitative measurement with acceptable precision and accuracy, typically defined as the concentration where the coefficient of variation falls below 20%. The LOQ is always higher than the LOD. Between the LOD and LOQ the analyte can be detected but not reliably measured.
- Definition basis
- Coefficient of variation below 20%
- Relation to LOD
- Always higher than the limit of detection
- Zone between LOD and LOQ
- Analyte detectable but not reliably measurable
- Used for
- Method validation, fitness for purpose
Common questions
Why can't a result between the LOD and LOQ be reported as a quantitative value?+
In that range the assay can confirm the analyte is present but the measurement's precision has not been demonstrated to meet the accuracy criteria required for a numeric result. Reporting a number from this zone would overstate the confidence a lab can actually place in it, so such results are typically reported as detected but not quantifiable.
How is the LOQ established during method validation?+
Analysts typically run replicate measurements of low-concentration standards and calculate the concentration at which the coefficient of variation first drops below the chosen threshold, often 20%. This is done alongside other validation parameters such as linearity, accuracy, and the limit of detection, following the lab's accreditation requirements.
Related terms
- Limit of Detection (LOD)
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- Negative Control
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- Positive Control
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- Repeatability
- The agreement between successive measurements of the same specimen made by the same analyst, on the same instrument, in the same laboratory,...
- Reproducibility
- The closeness of agreement between measurements obtained under changed conditions: different analysts, different instruments, different laboratories, or different times. A wider measure...
- Robustness
- The capacity of a method to remain unaffected by small, deliberate variations in its operating parameters, such as slight changes in temperature,...
- Selectivity
- The ability of a method to measure the target analyte specifically, even when other substances that might plausibly appear in a real...
Explained in these topics
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