The limit of detection concerns whether a method can distinguish a small amount from its background. The limit of quantification concerns measuring an amount with specified acceptable performance. Detection and reliable numerical measurement are different questions.
| Label | Analytical question | Avoid this assumption |
|---|---|---|
| LoD / detection limit | Can the method distinguish the target from background under defined conditions? | Not detected proves that absolutely none is present. |
| LoQ / quantification limit | Can an amount be measured with the required performance? | Every detected signal has an equally reliable exact number. |
| Clinical decision limit | How is a measurement used for a particular clinical question? | An analytical limit is automatically a clinical cutoff. |
Keep the wording and symbols intact
A report may use “not detected”, “detected below quantification”, a less-than sign or a laboratory-specific comment. These expressions should be preserved when taking notes. Replacing a qualified result with zero or with an invented midpoint removes information about what the method could establish.
Definitions in metrology and analytical-method guidance distinguish detection from quantification. Exact performance criteria and reporting conventions depend on the method and specimen. The cited FDA laboratory manual explains analytical terminology; it is not a universal reporting instruction for every medical assay.
Why a small signal may not have an exact value
An instrument has background variation, and a method has a validated working range. Recognising a signal and assigning it a sufficiently dependable numerical amount require different evidence. A result’s reporting precision should not be inferred simply from the number of digits a machine can display.
If a portal displays a boundary instead of a numerical result, ask whether that is an analytical reporting limit, a clinical decision limit or another category. Do not compare two laboratories’ less-than statements as though both used the same method and boundary.
A practical reading sequence
- Copy the full test and specimen names.
- Retain “less than”, “below” and “not detected” wording.
- Keep the unit, method note and report legend.
- Ask what limit the laboratory is referring to.
- Let the clinician explain what the qualified result can and cannot answer.
Suppose a fictional teaching report says “Marker Q: detected, below quantification”. The correct transcription keeps that whole phrase. Writing an exact amount would invent information. This example is about report notation, not a real marker or a diagnostic threshold.
Do not turn a method limit into a health verdict
A laboratory result still has to be interpreted for the reason the test was requested. This article does not establish whether a particular result rules anything in or out, whether another test is needed, or whether care can be delayed. Ask the issuing laboratory to clarify its wording rather than applying a generic internet conversion.
Scope and authorship
This is general adult report-reading education, not personal medical advice, diagnosis or treatment. The clinician responsible for your care must interpret individual results. Follow direct urgent instructions rather than waiting for an online explanation.
Prepared with AI assistance for DoubtPay; checked against linked sources. Not reviewed by a clinician.
Start with the basic blood-test report guide or browse the Medical blog. View Report Samjho and its current terms.