Medical Device Accessory Classification: EU MDR and FDA Pathways

How accessories are classified separately from parent devices under EU MDR Article 2(2) and FDA 513(f)(6), with examples, MDCG 2021-24 Rev.1 updates, and FDA's 2025-2026 reclassification initiative.

A medical device accessory is an article that is not itself a medical device but is intended to be used together with one or more specific devices to enable or assist their medical function. Under both EU and US regulations, accessories are treated as devices in their own right — but their classification does not automatically follow the parent device. Getting this wrong can mean choosing the wrong conformity assessment pathway, engaging a Notified Body unnecessarily, or, conversely, under-scoping your regulatory obligations.

This guide explains how the EU MDR and FDA each define, classify, and regulate accessories, what changed in the MDCG 2021-24 Rev.1 classification guidance (April 2026), and what the FDA's December 2025 request for public comment on accessory reclassification means for manufacturers.

What Is a Medical Device Accessory?

EU MDR Definition

Article 2(2) of Regulation (EU) 2017/745 defines an accessory for a medical device as:

"an article which, whilst not being itself a medical device, is intended by its manufacturer to be used together with one or several particular medical device(s) to specifically enable the medical device(s) to be used in accordance with its/their intended purpose(s) or to specifically and directly assist the medical functionality of the medical device(s) in terms of its/their intended purpose(s)."

Two elements must be present for a product to qualify as an accessory under this definition:

It is not itself a medical device. The accessory does not have an independent medical purpose. Its purpose is defined by the parent device(s) it supports.
It is intended by its manufacturer to be used together with specific medical device(s). The intended use must name the parent device(s) or a defined category of devices, and the accessory must either enable the parent device to function as intended or directly assist its medical functionality.

The definition is intentionally broad. It captures items such as surgical instrument trays designed for a specific implant system, docking stations for insulin pumps, protective covers for imaging heads, battery packs that power active devices, and software that configures or calibrates a parent device. At the same time, not every product used "with" a device qualifies. A general-purpose USB cable, for example, is not an accessory just because it can connect to a medical device, unless the manufacturer specifically intends it for that purpose.

FDA Definition

Under section 201(h) of the FD&C Act, the definition of "device" includes accessories. The FDA's 2017 guidance, Medical Device Accessories — Describing Accessories and Classification Pathways, elaborates: an accessory is "a finished device that is intended to support, supplement, and/or augment the performance of one or more parent devices."

The FDA's framework parallels the EU's in treating accessories as devices, but it adds a crucial policy principle: accessories should be classified based on their own risks, not automatically assigned the classification of the parent device. This principle was codified by the 21st Century Cures Act (2016) and the FDA Reauthorization Act (FDARA, 2017).

Accessory vs. Component vs. Part for Replacement

One of the most common sources of confusion is the boundary between an accessory, a component, and a replacement part. The distinction matters because components are not separately regulated devices, while accessories are.

Factor	Component	Accessory	Replacement Part
Regulatory status	Part of a finished device, not a standalone device	Treated as a device in its own right	May be a device if it significantly changes performance
Sold separately	Typically not — incorporated during manufacture	Yes — marketed for use with a parent device	Yes — sold to replace worn or damaged parts
Classification	None independently — covered by parent device classification	Classified separately under Annex VIII or FDA classification rules	Article 23(2) MDR: a replacement part that significantly changes performance, safety, or intended purpose is treated as a device
CE marking	No	Yes, if required by its own classification	Depends on whether it meets the Article 23(2) threshold
Examples	Internal circuit board, housing shell	Electrosurgical return electrode, endoscope light source, app that controls an infusion pump	Replacement battery for a defibrillator, new cutting bur for a surgical drill

Under MDR Article 23(2), items intended specifically to replace a part or component — and that do not significantly change the device's performance or intended purpose — are generally treated as replacement parts and may not require separate conformity assessment. However, if the replacement does significantly alter performance or safety characteristics, it is regulated as a device in its own right.

EU MDR: How Accessories Are Classified

Separate Classification Is Mandatory

MDR Annex VIII, implementing rule 3.2, states:

"If the device in question is intended to be used in combination with another device, the classification rules shall apply separately to each of the devices. Accessories for a medical device shall be classified in their own right separately from the device with which they are used."

This means an accessory must be evaluated against all 22 classification rules in Annex VIII using its own characteristics — duration of contact, invasiveness, whether it is active, the body system it interacts with — not those of the parent device.

Practical Classification Workflow

Confirm the product meets the Article 2(2) definition of an accessory. If the product has an independent medical purpose, it is a device in its own right, not an accessory.
Identify the intended use and technical characteristics of the accessory alone: Does it contact the patient? How long? Is it invasive? Is it active? Does it administer or exchange energy?
Apply the 22 classification rules in Annex VIII, Chapter III, to the accessory's own characteristics.
If multiple rules apply, select the strictest (implementing rule 3.5).
Check whether the resulting classification exceeds the parent device's class. This is generally discouraged but not prohibited; the MDCG classification guidance notes that accessories "should not be classified higher than the parent device" in most cases, but there are exceptions.

Exception: Active Implantable Accessories

Rule 8, indent 6 of Annex VIII states that active implantable devices and their accessories are classified as Class III. This is the one major exception where the accessory automatically receives the same classification as the parent device. For example, a programming wand used exclusively with a cardiac pacemaker is Class III regardless of its own characteristics, because the pacemaker is an active implantable device.

MDCG 2021-24 Rev.1 (April 2026)

The MDCG published Revision 1 of its classification guidance in April 2026, the first update since October 2021. While the revision does not change the implementing rules themselves, it adds clarifications that affect accessory classification:

Additional special cases beyond medical device software (MDSW) and Annex XVI products, including custom-made devices, devices manufactured and used within healthcare institutions, and the device part in single integral combination products.
Clarification on Rule 8 (implantable devices) and Rule 12 (active devices administering energy or substances), both of which frequently apply to accessories.
Terminology alignment — the term "surgical" was replaced with "clinical" in the context of invasive/implantable device definitions, and "device" was replaced with "product" in several classification rule tables for consistency.
Revised classification examples and new practical notes for Rules 2, 8, 9, 10, 12, 16, and 22, including updated examples for AED pads/electrodes and their classification as accessories versus integral components.

Classification Examples

Accessory	Parent Device	Accessory Classification	Rule Applied
Electrosurgical return electrode	Electrosurgical unit	Class IIa	Rule 11 (active device administering energy) or Rule 9 (invasive, transient)
Endoscope light source	Flexible endoscope	Class I or IIa	Rule 12 (active device), depends on whether energy is exchanged
Protective cover for ultrasound probe	Ultrasound scanner	Class I	Non-invasive, not active, low risk
Smartphone app that configures infusion pump parameters	Infusion pump	Class IIa (software)	Rule 11 (active therapeutic device)
Battery pack for cochlear implant processor	Cochlear implant (active implantable)	Class III	Rule 8, indent 6 (active implantable accessory — automatic Class III)
Surgical instrument tray for knee replacement system	Knee implant	Class I	Rule 8 indent 3 (reusable surgical instrument = Class I) or higher depending on invasiveness

FDA: How Accessories Are Classified

Independent Classification Policy

Since the 21st Century Cures Act (2016), FDA policy has been clear: accessories should be classified based on their own risks and the regulatory controls necessary to provide reasonable assurance of safety and effectiveness, not by reference to the parent device's class.

In practice, however, many accessories were historically classified alongside their parent devices through the 510(k) process, meaning a low-risk accessory for a Class III device might itself be treated as Class III simply by association. The Cures Act and FDARA created pathways to address this.

Pathways for Accessory Classification

Scenario	FDA Pathway	Description
New accessory with no predicate	De Novo classification (section 513(f)(2))	Submit a De Novo request proposing Class I or II. If granted, the accessory gets its own classification regulation and product code, which then serves as a predicate for future 510(k)s. Required to use eSTAR since October 1, 2025.
New accessory alongside a parent device 510(k)	Classification within the parent submission	When an accessory is submitted as part of the same 510(k) as its parent device, FDA classifies it within that review. The accessory receives its own product code.
Existing accessory with its own classification	Standard 510(k) or exemption	If the accessory already has its own classification regulation, it follows the same pathway as any other device in that class.
Existing accessory classified based on parent device, seeking lower classification	Accessory Classification Request (section 513(f)(6)(D)(ii))	Manufacturer or importer with existing marketing authorization submits a standalone request for reclassification. FDA has 85 days to respond.

FDA's December 2025 Request for Public Comment

On December 5, 2025, CDRH issued a request for public comment on existing medical device accessories that may be suitable for distinct classification into Class I (Docket No. FDA-2025-N-6224). The comment period was extended by 30 days and closed on March 5, 2026.

This initiative is part of FDA's ongoing effort to identify accessories that have been classified at a higher level than their own risk profile warrants, simply because they were historically tied to a higher-class parent device. The agency intends to consider all comments to develop a proposal for distinct Class I classification actions.

For accessory manufacturers, this is significant because:

A Class I designation with general controls only means the accessory would be exempt from 510(k) requirements (unless specifically required by regulation).
Cost savings are substantial. Companies would no longer need to prepare and submit 510(k) notifications for these accessories, reducing time-to-market and regulatory costs.
The process is ongoing. FDARA requires FDA to issue proposed lists of accessories suitable for Class I classification at least every five years. The 2019 final list classified several accessory types into Class I, and the current initiative suggests a new list is forthcoming.

2026 Reclassifications

FDA's reclassification table shows four reclassifications completed in 2026 so far, all from Class III to lower classes:

Optical diagnostic devices for melanoma detection (product code OYD) — reclassified
Electrical impedance spectrometers (product code ONV) — reclassified
Non-invasive bone growth stimulator (product code LOF) — reclassified
Ultrasound and muscle stimulator (product code LPQ) — reclassified

While not all of these are accessories, the trend confirms FDA's willingness to apply lower classification where the risk profile supports it.

Conformity Assessment for Accessories

EU MDR

Under the MDR, accessories are treated identically to medical devices for conformity assessment purposes (Article 1(4)). The conformity assessment pathway depends on the accessory's own classification:

Accessory Class	Conformity Assessment Route	Notified Body Required?
Class I	Self-declaration (Annex IV or Article 52(7))	No (except Class Is, Im, Ir)
Class IIa	Annex IX, or Annex XI Part A, or Annex XI Part B	Yes
Class IIb	Annex IX, or Annex X + XI Part A	Yes
Class III	Annex IX (full QMS + technical doc review)	Yes

If the accessory is supplied as part of a system or procedure pack, the rules of Article 22 may also apply.

FDA

Under the FDA framework, the pathway depends on the accessory's own classification:

Class I accessories with 510(k) exemption: register, list, and comply with general controls (QMSR, labeling).
Class II accessories: submit a 510(k) (or claim exemption if applicable).
Class III accessories: PMA pathway applies.

An accessory with its own product code and classification regulation follows the standard pathway for that class, independent of the parent device.

Technical Documentation Requirements

For EU MDR, accessories require their own technical documentation per Annex II and Annex III, just as any medical device would. Key elements include:

Intended use and indication specifying the parent device(s) the accessory supports.
General Safety and Performance Requirements (GSPR) evidence applicable to the accessory's own risk profile.
Risk management file (ISO 14971) addressing risks specific to the accessory, not just risks arising from its interaction with the parent device.
Clinical evaluation proportionate to the accessory's classification and risk.
Post-market surveillance plan scaled to the accessory's class.
IFU and labeling that clearly identify compatible parent devices and any limitations.

Under FDA requirements, accessories included in a parent device 510(k) are documented within that submission. Accessories with their own classification require standalone submissions with full device description, performance testing, and labeling.

Common Pitfalls

Assuming the accessory follows the parent device's class. This is the single most common error. Under both EU MDR and FDA frameworks, accessories must be classified independently. A Class III implant system may have accessories that are Class I or Class IIa.

Confusing accessories with components. Components are parts of the finished device that are not independently marketed. Accessories are separately marketed products. The regulatory treatment is fundamentally different.

Overlooking the active implantable exception. Under MDR Rule 8, indent 6, accessories for active implantable devices are automatically Class III. This overrides the normal separate-classification principle and can catch manufacturers off guard.

Not claiming Class I when eligible. Many accessories, particularly non-invasive, non-active items, may qualify as Class I under the MDR or be suitable for Class I designation under FDA rules. Failing to evaluate this means taking on unnecessary regulatory burden.

Ignoring the FDA's reclassification initiatives. If you manufacture an accessory that was historically tied to a higher-class parent device, the current FDA comment period and periodic list reviews offer a pathway to reduce regulatory burden. Monitor docket FDA-2025-N-6224 for outcomes.

Key Takeaways

Accessories are classified separately from the parent device under both EU MDR and FDA rules.
Under the MDR, apply all 22 Annex VIII rules to the accessory's own characteristics; the strictest applicable rule wins.
The one major exception: accessories for active implantable devices are always Class III under Rule 8, indent 6.
FDA pathways (De Novo, Accessory Classification Request, 510(k)) allow accessories to obtain or change their classification independently.
The MDCG 2021-24 Rev.1 (April 2026) added classification clarifications and a decision tree for borderline cases.
FDA's December 2025 public-comment initiative signals forthcoming proposals for reclassifying existing accessories into Class I, potentially eliminating 510(k) requirements for qualifying products.

Sources

Regulation (EU) 2017/745 (MDR), Article 1(4), Article 2(2), Annex VIII implementing rules 3.2–3.5.
MDCG 2021-24 Rev.1, Guidance on classification of medical devices, April 2026. Available at: health.ec.europa.eu.
FDA, Medical Device Accessories — Describing Accessories and Classification Pathways, December 2017.
21st Century Cures Act, Pub. L. 114-255, section 3060 (2016).
FDA Reauthorization Act (FDARA), Pub. L. 115-52, section 510 (2017).
Federal Register, Medical Devices; Classification of Accessories Distinct From Other Devices; Finalized List of Accessories Suitable for Class I, April 12, 2019.
FDA, Request for Public Comment on Existing Medical Device Accessories for Distinct Classification, December 5, 2025 (Docket No. FDA-2025-N-6224).
FDA Reclassification Table, current through April 16, 2026. Available at: fda.gov/about-fda/cdrh-transparency/reclassification.
Casus Consulting, EU MDR & IVDR Guide: Medical Device Accessories, Parts, Components, 2026.
Hogan Lovells, Call for Comments: FDA Wants Feedback on Distinct Classification of Device Accessories into Class I, January 2026.