Applying the 22 MDR Classification Rules and Implementation Rules

1. Key takeaways

The key to working through the 22 classification rules is not finding one rule that fits. It lies in the five implementing rules of Annex VIII: accessories are classified in their own right (3.2); software follows the device it drives or influences, or is classified in its own right when standalone (3.3); and where several rules apply simultaneously, the strictest rule and sub-rule that result in the higher classification prevail (3.5). The classification reasoning must exclude the rules one by one; citing only the applicable rule is not sufficient. These implementing rules are the layer where most classification errors occur, because they decide how combinations, accessories and software interact with the headline rules, and because the highest-classification principle turns a partial analysis into an incomplete one without the author noticing.

2. Legal basis

3. Expert insights

Insight 1: The highest-classification principle of implementing rule 3.5 is the step most often missed.

Where several rules, or several sub-rules within one rule, apply simultaneously to the same device, the strictest rule and sub-rule that result in the highest classification apply. The practical consequence is that demonstrating a Class IIa outcome under one rule is not enough. The manufacturer must also demonstrate that the other rules do not apply, or that they apply but do not produce a higher class. Classification reports that only document the applicable rule are a frequent reason for notified bodies to return the file. The discipline required is simple to state and demanding to execute: every rule must be addressed, and the address must be a reasoned statement, not a blank row in a table. Experience from review cycles shows that the rules most often left unexamined are those adjacent to the applied one, precisely because they appear unlikely to matter, and it is exactly there that a second reading sometimes produces a higher class.

Insight 2: Implementing rule 3.2 requires accessories to be classified in their own right.

An accessory does not automatically inherit the class of the device it is used with; it must be assessed independently through the rules. An accessory to a Class III device can perfectly well fall into Class IIa, and the reverse is equally possible. This surprises manufacturers who assume that a family of products shares one class, and it matters commercially: the accessory may need its own assessment route, its own technical documentation and its own notified body involvement even though it is sold alongside a device that has already been certified. Planning the family as a single certification block without checking rule 3.2 first creates schedule risk. The safer approach is to classify the accessory at the same time as the host device, in the same report, so that the two conclusions and the relationship between them are documented from the outset.

Insight 3: Implementing rule 3.3 provides two routes for software.

Software that drives a device or influences the use of a device falls within the same class as that device. Software that is independent of any other device is classified in its own right. Where this rule is used together with Rule 11, the higher classification applies. A single software product can therefore trigger both routes at once, for example when it drives a certified infusion pump and also carries standalone monitoring functions, and the final class is set by the higher of the two outcomes. The route decision must be documented explicitly, because it changes which evidence set the notified body will examine. In practice, the analysis should record the intended purpose against each route, the class produced by each, and the final class under the highest-classification principle, so that a reviewer can reconstruct the outcome without repeating the exercise.

Insight 4: Article 51(2) is the exit for classification disputes, but the price is time.

Where the manufacturer and the notified body disagree on the classification, the dispute is referred to the competent authority of the Member State in which the manufacturer has its registered place of business. While the referral is pending, the project stands still. This is why the front-loaded investment in classification reasoning is cheaper than remediation afterwards: a report that anticipates the objections of the notified body, addresses every rule and applies the highest-classification principle correctly removes most grounds for dispute before the assessment even starts. Companies should treat the referral procedure as a genuine but costly instrument, and design their documentation so they rarely need it. Where a dispute does arise, the request to the competent authority should include the full classification matrix, the reasoning for each rule and the notified body’s contrary position, so that the authority receives a complete picture in one submission and the procedure is not extended by repeated requests for information.

4. Practical recommendations

1. Use a full 22-rule matrix format for the classification report, with columns for rule number, applicability, sub-rule, conclusion and reasoning.
2. For every rule recorded as not applicable, state the reason; never leave blank rows or skip silently.
3. Issue separate classification conclusions for accessories, software and combination products, then merge them under rule 3.5 by taking the highest class.
4. When a classification conclusion changes, trigger a synchronised update of the technical documentation, the UDI data and the labelling.
5. Where a dispute with the notified body arises, initiate the Article 51(2) procedure early and prepare an alternative route in parallel.

5. Verification checklist

• □ The classification report contains the complete 22-rule matrix
• □ Every non-applicable rule has a stated reason
• □ Accessories have been classified separately under 3.2
• □ The software route (driving or standalone) has been determined under 3.3
• □ The strictest rule has been adopted as the final conclusion under 3.5
• □ The conditions for initiating the Article 51(2) dispute procedure have been recorded

Regulatory information verified as of 29 October 2026.

About GRZAN. GRZAN helps manufacturers apply the classification rules of Annex VIII to Regulation (EU) 2017/745 correctly, including the implementing rules that decide accessories, software and multi-rule cases. We build the 22-rule classification matrix, defend it in notified body dialogue and resolve classification disputes through Article 51(2) when they arise. For a reliable classification and CE marking route in the European Union under the EU MDR, contact info@grzanglobal.com.