Result qualification · O-024
Methods, specifications, detection limits and uncertainty
A number needs its method and decision rule. Specifications define the criterion; detection limits and measurement uncertainty define how much confidence the reported result can carry.
An analytical result is interpretable only when the report identifies the method, measurand, units, specification and relevant performance limits. “Not detected” means the result fell below the method's detection capability for that analyte and sample, while measurement uncertainty describes the range of values reasonably attributable to the measurand; neither phrase means absolute certainty.
Method validation shows that a procedure is fit for its intended purpose. It does not make the procedure fit for every analyte, matrix, concentration range or decision.
Five terms that should not be collapsed
| Term | Plain-English meaning | Common error |
|---|---|---|
| Method | The documented procedure used to make the measurement. | Naming an instrument as if it were a complete procedure |
| Specification | The acceptance criteria applied to a material or product. | Treating a lab result as a pass without a stated criterion |
| Limit of detection (LOD) | The lowest level at which detection is supported under the method. | Reading a non-detect as zero |
| Limit of quantitation (LOQ) | The lowest level at which a quantitative result has suitable performance. | Reporting an exact amount below the quantitative capability |
| Measurement uncertainty | A parameter describing the dispersion reasonably attributable to the measured value. | Treating the displayed digits as exact |
How should “not detected” be written?
Why does uncertainty matter near a limit?
A reported value can sit close to an acceptance limit. The laboratory's decision rule should explain how it considers measurement uncertainty when declaring conformity. Without that rule, readers may treat a borderline result as more certain than the method supports.
Use the form result ± expanded uncertainty only when the report defines the coverage and units. Do not invent an uncertainty from the number of decimal places.
More digits do not create more certainty. The validated method and uncertainty evaluation determine the defensible precision.
What does method validation examine?
- Specificity or selectivityCan the procedure distinguish the target from relevant interferences?
- Accuracy and precisionHow close and repeatable are results across the intended range?
- Range and responseDoes the procedure perform across the concentrations used for decisions?
- Detection and quantitation capabilityCan the method detect or measure the target at the levels claimed?
- Robustness and controlsDo small controlled changes, system suitability and quality controls support dependable operation?
Continue the evidence check
Questions readers ask
Does “not detected” mean the contaminant is absent?
No. It means the laboratory did not detect the named analyte above the method's detection limit in the tested sample. The report should state the analyte, method, matrix and limit; compounds outside the panel remain unassessed.
What is the difference between LOD and LOQ?
The limit of detection supports a decision that a signal is distinguishable from the relevant blank or noise. The limit of quantitation supports a numerical result with suitable performance. A method may detect an analyte at a level too low to quantify with dependable accuracy and precision.
Does a pass specification prove safety?
No. A pass means the reported result met the stated acceptance criterion under the applied decision rule. Safety depends on whether the right attributes, limits, sample and product context were chosen, plus clinical and regulatory evidence outside the laboratory result.
Should every COA show measurement uncertainty?
Reporting conventions differ, and qualitative or some routine results may not display a numeric uncertainty on the certificate. The laboratory should still understand uncertainty where it affects validity or conformity decisions and should explain the decision rule when a result lies near a limit.
Primary sources and update triggers
- Eurachem: The Fitness for Purpose of Analytical Methods: method validation, detection capability, precision and fitness for purpose
- Eurachem/CITAC: Quantifying Uncertainty in Analytical Measurement: framework for evaluating and expressing uncertainty
- EMA: ICH Q2(R2) Validation of Analytical Procedures: validation for identity, assay, purity, impurities and other intended analytical purposes
Editorial experience
From our work: how we checked this page
For topical-map item O-024, Methods, specifications, detection limits and uncertainty was checked as a distinct editorial task, not treated as a generic peptide page. We reviewed 3 unique external sources and 7 internal destinations in the page, then checked that the opening answer, headings, source descriptions and linked next steps stayed within the same claim boundary. The count records links in the published page and is not a claim that every source carries equal evidential weight.
Eleni Kiromitis checked the laboratory and scientific wording, drawing on direct experience commissioning laboratory tests and reviewing certificates of analysis and chromatograms. She checked whether each method was matched to the attribute it can measure, whether sample and batch limits remained visible, and whether the conclusion stopped where the analytical record stopped. Yianni Kiromitis retained responsibility for source verification, editorial decisions and correction management.
We did not use patient experience, a personal treatment outcome, seller testimony or an assumed product identity to support this page. The publication did not independently test a vial for this review. Where a page refers to a laboratory result, that result applies only to the named sample, method and attribute. We kept uncertainty beside the conclusion, recorded which source supports each material claim, and checked that the visible review date matches the publication record. A new controlled study, regulator update, corrected source, analytical report or credible safety signal can trigger reassessment through the public correction route.