IMDRF Codes: Adverse Event Terminology Guide

Medical device post-market surveillance (PMS) and vigilance reporting require standardized terminology to detect safety signals across jurisdictions. The International Medical Device Regulators Forum (IMDRF) Adverse Event Terminology (IMDRF/AE WG/N43) provides this global architecture, harmonizing US FDA MedWatch Form 3500A submissions and European Union Manufacturer Incident Reports (MIR v7.3.1).

Notice: This technical regulatory reference provides information on medical device adverse event terminologies for regulatory affairs and quality professionals; it does not provide clinical or medical advice.

What it is

IMDRF codes comprise a standardized dictionary of alphanumeric terms and definitions categorizing every aspect of a medical device adverse event. Maintained by the IMDRF Adverse Event Terminology Working Group (AE WG), this system replaces fragmented national vocabularies with a unified ontology mapped to the National Cancer Institute Thesaurus (NCIt).

The terminology covers the full incident lifecycle: device malfunctions, components, investigation methods, laboratory findings, root causes, and clinical outcomes.

Regulatory authorities mandate IMDRF coding in electronic submission portals. In the United States, the FDA Center for Devices and Radiological Health (CDRH) requires IMDRF codes for electronic Medical Device Reporting (eMDR) via the FDA Electronic Submissions Gateway (ESG NextGen) Unified Submission Portal. In the European Union, Competent Authorities mandate IMDRF codes in Manufacturer Incident Reports under EU MDR (Regulation (EU) 2017/745) and IVDR (Regulation (EU) 2017/746), adhering to MDCG guidance documents. For digital health, adverse event coding interfaces with Software as a Medical Device (SaMD) clinical evaluation to track software anomalies and cybersecurity incidents.

Who runs it and what it covers

Governed by the International Medical Device Regulators Forum (IMDRF), participating authorities include the US FDA, European Commission, Health Canada, Japan PMDA, Australia TGA, Brazil ANVISA, and the UK MHRA. Technical maintenance is directed by document IMDRF/AE WG/N44 through scheduled annual update cycles.

In this lexicon, “Device” denotes any medical device, IVD, accessory, or component. “Patient” encompasses patients, operators, or any individual affected. All definitions observe American English spelling.

The framework organizes adverse event data across seven discrete categories, designated Annexes A through G:

Annex A: Medical Device Problem (A codes): Malfunctions, failures, and usability issues.
Annex B: Cause Investigation – Type of Investigation (B codes): Testing methods, visual inspections, or software audits.
Annex C: Cause Investigation – Investigation Findings (C codes): Empirical laboratory findings (e.g., fatigue fracture, electrical short).
Annex D: Cause Investigation – Investigation Conclusion (D codes): Final root-cause determination (e.g., manufacturing defect, user error).
Annex E: Health Effects – Clinical Signs and Symptoms or Conditions (E codes): Signs, symptoms, or clinical disorders in the affected person.
Annex F: Health Effects – Health Impact (F codes): Clinical consequences and required interventions (e.g., surgical revision, hospitalization).
Annex G: Medical Device Component (G codes): Specific part, subassembly, or sensor involved.

Annexes A and G represent “device codes,” Annexes E and F represent “patient codes,” and Annexes B, C, and D are designated “evaluation codes.”

IMDRF Annex A: Medical Device Problem Codes

IMDRF Annex A classifies observable device failure modes across more than 20 Level 1 categories (A01–A24), branching into granular child codes. Core categories include:

A01 (Material/Chemical Integrity): Degradation, corrosion, leaching, and biocompatibility issues.
A02–A08 (Mechanical Properties): Deformities, fracture, occlusion, unintended movement, and fluid leakage.
A09–A14 (Electrical, Firmware, Software): Power loss, unexpected resets, communication timeouts, and calculation errors.
A15–A24 (Packaging, Labeling, Usability): Sterile barrier breach, packaging defects, and interface confusion.

Reporters must adhere to the lowest-level leaf node rule: select the most granular applicable descendant code. Reporting both parent and child codes is redundant and rejected by submission gateways.

How to search or use it

Reporters identify codes using the online IMDRF Adverse Event Terminology Web Browser through seven steps:

Access Browser: Open the official IMDRF Adverse Event Terminology Web Browser portal.
Select Target Annex: Click the navigation tab for the relevant category (e.g., Annex A for device problems or Annex G for components).
Execute Dynamic Search: Type descriptive terms in the search field using American English spelling (e.g., “corrosion”, “occlusion”).
Navigate Hierarchies: Use “Expand all” or “Collapse all” buttons to explore parent-child levels down to specific subcategories.
Evaluate Matches: Review highlighted search terms displayed in red across code names and definitions.
Select Leaf Code: Choose the lowest-level applicable code without selecting its parent.
Record NCIt Mapping: Export the alphanumeric IMDRF code and its associated NCIt concept code for submission.

Submission rules vary by regulatory reporting role and gateway:

FDA Form 3500A (Section F10): Importers and facilities report Annexes A, G, E, and F. Without patient involvement, enter code 4582 (“No Clinical Signs, Symptoms or Conditions”) in Annex E and code 2645 (“No Patient Involvement”) in Annex F. If no part is identified, enter code 4755 (“Part/Component/Sub-assembly Term not Applicable”) in Annex G. Code 3189 is reserved for FDA internal use.
FDA Form 3500A (Section H6): Manufacturers must supply codes across all seven annexes. For active evaluations, enter code 4118 (“Type of Investigation Not Yet Determined”) in Annex B and code 3233 (“Results Pending Completion of Investigation”) in Annex C.
EU MIR v7.3.1: Manufacturers enter IMDRF codes into XML elements for EUDAMED vigilance transmission, evaluating incident rates against baseline data from the FDA Summary of Safety and Effectiveness Data (SSED).

Strengths and limits

Strengths:

Global Interoperability: Replaces disparate national vocabularies with a uniform standard adopted across FDA, Health Canada, TGA, and EU authorities.
High-Throughput Signal Detection: Standardized coding allows algorithms to detect emerging failure trends faster than unstructured text.
Multi-Axial Precision: Separates device problems (Annex A), components (Annex G), root causes (Annexes B–D), and health impacts (Annexes E–F).
Standards Alignment: Integrates with NCIt concept ontologies and complements ICH E2A clinical safety standards for combination products.

Limits:

Classification Complexity: Incidents involving interconnected software and hardware can lead to differing coding interpretations.
Update Latency: Emerging modalities, such as generative AI diagnostics, may lack dedicated leaf codes until annual N44 maintenance revisions.
Asymmetric Facility Data: Importers and hospitals rarely possess internal engineering failure data, requiring subsequent manufacturer investigation filings.

Alternatives

Medical device incident coding operates alongside several clinical and regulatory vocabularies:

System	Governing Body	Scope & Architecture	Primary Regulatory Use Cases
IMDRF Adverse Event Codes	IMDRF / AE Working Group	7 hierarchical annexes (A–G) covering device failures, components, investigations, and health effects.	Mandatory medical device adverse event reporting (FDA Form 3500A, EU MIR v7.3.1, EUDAMED).
FDA Legacy CDRH Codes	US FDA (CDRH)	Flat and 4-digit legacy event problem and evaluation codes.	Historical queries in the FDA MAUDE database; pre-harmonization legacy files.
MedDRA	ICH / MSSO	5-level hierarchy focused on biopharmaceutical adverse drug reactions and clinical diagnoses.	Pharmaceutical pharmacovigilance, clinical trial safety databases, and combination product trials.
SNOMED CT	SNOMED International	Comprehensive polyhierarchical clinical healthcare terminology.	Electronic Health Records (EHRs), clinical documentation, and hospital informatics.
NCIt	US National Cancer Institute	Biomedical reference ontology providing concept IDs and cross-mappings.	Underlying semantic reference model for FDA and IMDRF code definitions.

While MedDRA and SNOMED CT govern clinical trials and health records, IMDRF terminology is the dedicated standard for medical device vigilance and failure analysis.

FAQ

What is the difference between IMDRF codes and MedDRA?
MedDRA classifies clinical conditions and drug reactions. IMDRF terminology is tailored for medical devices, offering dedicated hierarchies for physical malfunctions, components, and root causes alongside clinical effects.

Which IMDRF annexes are required on FDA MedWatch Form 3500A?
Section F10 requires four annexes for importers and facilities: Annex A (Device Problem), Annex G (Component), Annex E (Clinical Signs/Symptoms), and Annex F (Health Impact). Section H6 requires all seven annexes (A, G, B, C, D, E, F) for manufacturers.

How does IMDRF Annex A differ from Annex G?
Annex A identifies what went wrong functionally or structurally (e.g., “Leakage” or “Software Exception”). Annex G identifies the physical part involved (where it occurred, such as “Gasket” or “Capacitor”).

What codes are used when a device investigation is still ongoing?
Under FDA MDR rules, manufacturers submit placeholder codes 4118 (“Type of Investigation Not Yet Determined”) in Annex B and 3233 (“Results Pending Completion of Investigation”) in Annex C, followed by a supplemental report when complete.

Are IMDRF codes mandatory for EU MDR Manufacturer Incident Reports?
Yes. European vigilance reporting mandates the Manufacturer Incident Report (MIR v7.3.1) under EU MDR 2017/745 and IVDR 2017/746, requiring IMDRF coding across device problems, investigation findings, components, and health impacts.

Can multiple IMDRF codes be assigned to a single incident report?
Yes. If a device experienced multiple failure modes or clinical symptoms, reporters can assign multiple codes across relevant annexes. However, reporters must select only lowest-level leaf codes without duplicating parent terms.

Sources

US Food and Drug Administration (FDA). “MDR Adverse Event Codes.” Published August 21, 2026; updated April 13, 2026. https://www.fda.gov/medical-devices/mandatory-reporting-requirements-manufacturers-importers-and-device-user-facilities/mdr-adverse-event-codes
US Food and Drug Administration (FDA). “How to Code an MDR Adverse Event Report.” Updated April 13, 2026. https://www.fda.gov/medical-devices/mdr-adverse-event-codes/how-code-mdr-adverse-event-report
International Medical Device Regulators Forum (IMDRF) Adverse Event Terminology Working Group. “IMDRF Terminologies for Categorized Adverse Event Reporting (AER): Terms, Terminology Structure and Codes (IMDRF/AE WG/N43).” Accessed November 10, 2026. https://www.imdrf.org/working-groups/adverse-event-terminology/imdrf-adverse-event-terminology-web-browser
European Commission / Medical Device Coordination Group (MDCG). “Manufacturer Incident Report (MIR) for Mandatory Vigilance Reporting (v7.3.1) and MDCG Vigilance Guidance.” Accessed November 10, 2026. https://ec.europa.eu/health/medical-devices-sector/vigilance-and-post-market-surveillance_en