STATISTICS
One material and one run are enough: That design measures a narrow repeatability condition and can materially understate routine variation.
More decimal places improve the claim: They often advertise sampling noise. Limits should be rounded to the resolution supported by the experiment and reporting system.
Limitations and interpretation cautions Estimated limits vary because they are statistics calculated from a certain number of samples. A different set of blanks or low pools will not reproduce exactly the same value. Confidence intervals or resampling can make this uncertainty visible, especially when a claim lies close to a required specification. Verification should also account for lot-to-lot or site-to-site variation if those conditions matter to the intended claim. The usual ordering LoB < LoD < LoQ
is conceptually helpful but should not be imposed by arithmetic manipulation. An apparent reversal can indicate mismatched definitions, unsuitable criteria, sparse data, rounding or model failure. It should trigger review of the design and claim rather than relabelling the values. Likewise, an LoQ below the LoD is difficult to interpret for a conventional continuous quantitative assay. A number cannot credibly be quantified
Patient samples are often the ideal matrix but may be difficult to obtain at exact low
concentrations; in which case pools, dilutions or spiked materials can be justified
at a concentration that is not reliably distinguished from blank under the stated framework. Low-end capability is also conditional
on the measurement system remaining stable. Carryover, contamination, reagent background, calibration drift and software censoring can alter the distributions. Routine quality processes should therefore protect the conditions under which the limits were established, without pretending that ordinary internal quality control alone re-estimates LoB, LoD or LoQ.
PPi
Practical take home points Name the limit: “Analytical sensitivity” without LoB, LoD or LoQ is ambiguous. Start with the question – blank discrimination, reliable detection or acceptable quantification. Predefine false-positive and false- negative probabilities for detection and performance criteria for quantitation.
Use representative materials and distribute replication across the conditions included in the claim. Inspect distributions, censoring and changing variance before choosing a Gaussian formula. Do not define LoQ through a universal CV threshold – justify what quantitative performance is needed. Translate the study into explicit reporting rules, especially for detected results below the LoQ. Report limits with units, conditions and sensible precision, and do not treat them as clinical decision limits.
References 1
Clinical and Laboratory Standards Institute. Evaluation of Detection Capability for Clinical Laboratory Measurement Procedures. 2nd edn. CLSI guideline EP17-A2. Wayne, PA: CLSI; 2012. Reaffirmed 2017.
2 Armbruster DA, Pry T. Limit of blank, limit of detection and limit of quantitation. Clin Biochem Rev. 2008 Aug; 29 Suppl 1:S49–52.
3 Linnet K, Kondratovich M. Partly nonparametric approach for determining the limit of detection. Clin Chem. 2004 Apr; 50 (4): 732–40. doi:10.1373/ clinchem.2003.029983.
4 Currie LA. Nomenclature in evaluation of analytical methods including detection and quantification capabilities. Pure Appl Chem. 1995; 67 (10): 1699–1723.
5
International Council for Harmonisation. ICH Q2(R2) Validation of Analytical Procedures. Geneva: ICH; 2023.
6 International Organization for Standardization. ISO 11843-1:1997. Capability of detection - Part 1: Terms and definitions. Geneva: ISO; 1997.
7 Westgard JO. Basic method validation and verification. 4th edn. Madison, WI: Westgard QC; 2020.
Routine quality processes should protect the conditions under which limits were established, without pretending that ordinary internal quality control alone re-estimates LoB, LoD or LoQ.
Dr Stephen MacDonald is Consultant Clinical Scientist, The Specialist Haemostasis Unit, Cambridge University Hospitals NHS Foundation Trust, Cambridge Biomedical Campus, Hills Road, Cambridge CB2 0QQ.
+44 (0)1223 216746 October 2026
WWW.PATHOLOGYINPRACTICE.COM 21
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