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    Adverse Event

    Any untoward medical occurrence in a subject, whether or not related to the device.

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

    Definition

    Per ISO 14155, an adverse event is any untoward medical occurrence, unintended disease or injury, or untoward clinical signs in subjects, users, or other persons, whether or not related to the investigational device. ISO 14155 asks sponsors to record all adverse events in a device investigation and to assess each for seriousness and for relationship to the device or procedure. Adverse device effects are the subset related to the device. Clinical investigation plans define how events are collected, coded (often with MedDRA) and adjudicated, and the results feed safety reporting and the final clinical investigation report.
    What the regulation says
    Regulators like the FDA and those operating under the EU MDR mandate the reporting of adverse events to ensure patient safety and device effectiveness. The FDA’s 21 CFR Part 803 outlines medical device reporting requirements, while the EU MDR (Regulation (EU) 2017/745) details vigilance and post-market surveillance obligations, including the reporting of serious incidents. ISO 14155, specifically clause 7, provides guidance on recording and reporting adverse events in clinical investigations.

    What this means in practice

    AEs are the foundational unit of clinical safety reporting. Serious AEs (SAEs) and device-related AEs (ADEs/SADEs) trigger expedited reporting obligations.

    Examples

    • A patient implanted with a cardiac pacemaker experiences an unexpected infection at the implant site, which is identified as an adverse event.
    • During a clinical trial for a new glucose monitor, a participant reports a localized skin rash at the sensor application site, constituting an adverse event.
    • A user of an insulin pump experiences a hypoglycemic episode that requires emergency medical intervention, categorized as a serious adverse event.
    Common pitfalls
    • •Confusing an adverse event with a device malfunction that did not lead to an adverse clinical outcome, as these have distinct reporting pathways.
    • •Failing to initiate an investigation or report an adverse event due to a perceived lack of direct causal link to the device, as all untoward occurrences must be assessed.
    • •Delaying the reporting of serious adverse events (SAEs) beyond the mandated regulatory timelines, which can lead to non-compliance.
    • •Not adequately documenting the assessment of causality between the device and the adverse event, which is critical for regulatory review.
    • •Inconsistently applying definitions of "serious" across different studies or reporting jurisdictions, causing reporting errors.

    Frequently asked questions

    An adverse event is any untoward medical occurrence, while a serious adverse event meets specific criteria, such as leading to death, a serious deterioration in health, or requiring hospitalization, as defined by regulations like the EU MDR Annex XVI and FDA 21 CFR 803.3.

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    Sources

    3 sources

    Every citation below opens the original document. Each is graded against our source-tier hierarchy so you can see what rests on binding law versus commentary.

    Tier 1Binding law and standards· 1Tier 2Regulator guidance and consensus· 1Tier 3Peer-reviewed and registry evidence· 1
    Link health: 3 verified· last checked 2026-06-20
    ISO·1FDA·1NIH·1
    1. 1
      ISO 14155 AE definitions
      Tier 1 Verified
      ISOiso.org
    2. 2
      FDA - Clinical Trials and Human Subject Protection
      Tier 2 Verified
      FDAfda.gov
    3. 3
      ClinicalTrials.gov
      Tier 3 Verified
      NIHclinicaltrials.gov

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