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    Clinical & TrialsClinical EvidenceLoD / LoQ

    Limit of Detection / Limit of Quantitation

    Lowest analyte concentrations an assay can reliably detect (LoD) or quantify (LoQ).

    Reviewed by Christian Espinosa, Founder, Blue Goat CyberLast reviewed May 5, 2026

    Definition

    LoD is the lowest concentration distinguishable from a blank with stated probability. LoQ is the lowest concentration that can be quantitatively measured with stated accuracy and precision (per CLSI EP17 / EP05). CLSI EP17 describes how to establish the limit of blank, LoD and LoQ using replicate testing across lots, instruments and days. The LoQ is often set where total error or imprecision meets a predefined goal. These values appear in the IFU and in performance evaluation evidence under IVDR and in FDA submissions, and matter most for assays used near clinical decision thresholds.
    What the regulation says
    Regulatory bodies like the FDA and organizations such as the Clinical and Laboratory Standards Institute (CLSI) require the establishment of Limits of Detection (LoD) and Quantitation (LoQ) for in vitro diagnostic (IVD) devices. These analytical performance characteristics, as described in documents like CLSI EP17 and EP05, are crucial for validating the claims of an IVD, particularly for assays where the detection and measurement of low analyte concentrations are clinically significant, such as in infectious diseases or oncology. Manufacturers must demonstrate that their assays can reliably detect and quantify analytes at these lower limits to ensure patient safety and effective treatment decisions, aligning with requirements in 21 CFR Part 809 for IVDs and principles seen in EU IVDR Annex I, General Safety and Performance Requirements.

    What this means in practice

    Critical performance characteristics for IVD claims, especially for infectious disease and oncology assays where low-burden detection drives clinical utility.

    Examples

    • An IVD manufacturer determines the LoD for its new HIV viral load assay to ensure it can detect very low levels of viral RNA in early infection, as required by FDA guidance.
    • A molecular diagnostic company establishes the LoQ for its oncology assay to precisely measure circulating tumor DNA fragments, guiding treatment selection and monitoring in cancer patients.
    • An assay for detecting bacterial pathogens in blood culture is validated with an LoD study to confirm its ability to identify low colony counts before clinical symptoms become severe.
    Common pitfalls
    • •Failing to establish LoD and LoQ using appropriate statistical methods can lead to invalid claims regarding assay sensitivity.
    • •Not re-evaluating LoD and LoQ after significant assay modifications can result in underperforming or non-compliant devices.
    • •Confusing LoD with clinical sensitivity can lead to misinterpretation of an assay's true diagnostic capability.
    • •Using inappropriate sample matrices for LoD and LoQ studies can invalidate the relevance of the established limits to real-world clinical use.
    • •Presenting a single LoD or LoQ value when different matrices or sample types require distinct limits is a common oversight.

    Frequently asked questions

    LoD and LoQ demonstrate an IVD's analytical sensitivity, ensuring it can reliably detect and measure analytes at low concentrations, which is critical for accurate diagnosis and patient management, especially in early disease detection or monitoring of minimal residual disease.

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    Sources

    3 sources

    Sources support the definition or relevant regulatory context, not necessarily every claim on this page. Each is graded against our source-tier hierarchy so you can see what rests on binding law versus commentary.

    Tier 1Binding law and standards· 2Tier 2Regulator guidance and consensus· 1
    Link health: 3 verified· last checked 2026-06-20
    CLSI·1ISO·1FDA·1
    1. 1
      CLSI EP17
      Tier 1 Verified
      CLSIclsi.org
    2. 2
      ISO 14155 Standard Page
      Tier 1 Verified
      ISOiso.org
    3. 3
      FDA - Clinical Trials and Human Subject Protection
      Tier 2 Verified
      FDAfda.gov

    Inline markers like [1] jump to the matching reference above.