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    Blinding and Masking

    Procedures that hide treatment assignment from patients, investigators, or assessors to reduce bias.

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

    Definition

    Single-, double-, and triple-blinding apply progressively to patients, investigators, and outcome assessors. Device trials often achieve only assessor-blinding due to the visible nature of devices/procedures.
    What the regulation says
    Blinding and masking are critical study design elements emphasized by regulatory bodies like the FDA in their guidance on clinical trials for medical devices, particularly to minimize bias. The EU MDR, in Annex I, Section 21.2, also stresses the importance of appropriate statistical methods and study design to ensure the scientific validity and reliability of clinical data. These practices aim to ensure objectivity in assessing treatment effects and patient outcomes.

    What this means in practice

    Independent core labs and blinded adjudication committees are standard mitigations for device trials where full blinding is impossible.

    Examples

    • A clinical trial for a novel implantable glucose monitor might blind the patients to whether they received the active device or a similar-looking placebo device that does not provide glucose readings.
    • In a study evaluating a surgical robot, the surgeons and patients may not be blind, but the outcome assessors evaluating post-operative complications and recovery time can be blinded to the treatment arm.
    • A study comparing two different drug-eluting stents might anonymize the stent type in patient records and blind the radiologists interpreting follow-up angiograms to stent assignment.
    Common pitfalls
    • •Failure to document the rationale for the chosen blinding level can lead to regulatory scrutiny.
    • •Inadequate blinding procedures can compromise the scientific validity of clinical trial results, leading to questions from regulatory authorities.
    • •Assuming that device trials cannot be blinded at all, rather than seeking opportunities for partial blinding, is a common pitfall.
    • •Not accounting for potential unblinding events and having a plan to address them can undermine study integrity.

    Frequently asked questions

    Blinding is challenging due to the visible nature of devices, the need for clinician interaction during procedures, and the distinct characteristics of device interventions compared to pharmaceutical products.
    Grouped by theme

    Primary references

    3 sources
    Link health: 3 verified· last checked 2026-06-20
    ICH·2ISO·1
    1. 1
      ICH E9
      Verified
      ICHich.org
    2. 2
      ICH Guidelines
      Verified
      ICHich.org
    3. 3
      ISO 14155 Standard Page
      Verified
      ISOiso.org

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