The different classes

Medical devices and accessories are classified in the European Union in accordance with the MDR, or more precisely in accordance with Annex VIII of Regulation (EU) 2017/745. The classification is based on 22 rules as well as relevant definitions and implementing provisions. The underlying idea is to differentiate medical devices according to their risk. The higher the risk, the higher the risk class. The following classes are defined:

Class I (low risk)
Class IIa (low to medium risk)
Class IIb (medium to high risk)
Class III (high risk)

In practice, the following classes are also distinguished:

Class Ir (reusable surgical instruments of class I)
Class Is (sterile devices of class I)
Class Im (devices of class I with measuring function)

These classes are not defined in this form in the MDR. For devices that are placed on the market in a sterile condition, for devices with a measuring function or for devices that are reusable surgical instruments, the manufacturer must apply the procedures listed in MDR Annex IX Chapter I and III or in Annex XI Part A. This means that a notified body is required for the conformity assessment. For this reason, an additional subdivision into Ir, Is and Im is made for class I devices that would otherwise not need a notified body.

Basics of classification

The application of the 22 rules described in Annex VIII to determine the classes for medical devices requires precise knowledge of the applicable definitions from the following sources:

Article 2 Definitions
Annex VIII Chapter I

In addition, the implementing provisions of Annex VIII Chapter II must be observed.

With these basics, the intended purpose of the medical device or an accessory is analyzed in order to determine which of the 22 rules are applicable and into which classes medical devices or accessories are to be classified accordingly. For this procedure, it is imperative that the intended purpose is available and that the work is carried out with the utmost care. Incorrect classifications can result in higher risk classes and thus in partially immensely higher costs. This should therefore be avoided!

Definitions

Annex VIII describes definitions that are relevant in addition to the definitions in Article 2. These could also have been included in Article 2, but are ultimately only relevant for classification and were therefore probably included in Annex VIII. The definitions are divided into two categories. In order not to reproduce the content of the regulation 1:1 at this point and instead to create informative added value for you, we only present a short excerpt. If you need the exact definitions, we will link the MDR further down in the article.

Duration of use
1. “Transient” means normally intended for continuous use for less than 60 minutes.
2. “Short-term” means normally intended for continuous use for between 60 minutes and 30 days.
3. “Long-term” means normally intended for continuous use for more than 30 days.
Invasive and active devices
1. “Body orifice” means any natural opening in the body, as well as the external surface of the eyeball, or any permanent artificial opening, such as a stoma.
2. “Surgically invasive device” […]
3. “Reusable surgical instrument” […]
4. “Active therapeutic device” […]
5. “Active device intended for diagnosis and monitoring” […]
6. “Central circulatory system” […]
7. “Central nervous system” […]
8. “Injured skin or mucous membrane” […]

Many of the classification rules refer to these definitions. You should therefore know those that are relevant to your device. We have observed that in some cases the classification as an invasive or active device according to the definition in Article 2 is already incorrect, and as a result the definitions from Annex VIII are also incorrectly applied.

Let’s look at the following example:

“Invasive device” means any device which, in whole or in part, penetrates inside the body, either through a body orifice or through the surface of the body [Source: MDR, Article 2]

Body orifice is not defined in Article 2 and is therefore often interpreted differently during the initial consideration than the definition in Annex VIII provides. You will find this a little further up in the list. If a product is incorrectly classified as an invasive product, this quickly results in a risk class from IIa, whereas a non-invasive product is classified in class I in many cases. It also becomes clear that one should know the definitions from both sources of the MDR.

Implementing rules

There are currently 7 implementing provisions mentioned in Annex VIII of the MDR. In terms of content, these are:

Classification according to intended purpose
Classification of connected devices and accessories
Classification of software
Classification of devices that are used on different parts of the body
Classification when several rules are applicable
Determination of the duration of use
Classification of devices that enable a direct diagnosis

You can find the exact wording for each implementing provision in the MDR. We have referenced these for you further down in the article.
We are observing an accumulation among manufacturers of class I with regard to the fifth implementing provision. In these cases, not all applicable rules are taken into account, but mostly the first applicable rule is used to determine the class of the medical device. However, if several rules are applicable, the ultimate class is the highest class of all applicable rules. However, this circumstance is largely known among manufacturers who already have medical devices of class IIa to III in their portfolio.

Classification rules

The 22 rules are divided into four categories:

Non-invasive devices (rules 1 to 4)
Invasive devices (rules 5 to 8)
Active devices (rules 9 to 13)
Special rules (rules 14 to 22)

If the device to be classified is a non-invasive device, rules 5 to 8 for invasive devices are not relevant in more detail. Nevertheless, you must check rules 6 to 22 for applicability, as the fifth implementing provision states that the highest classification is applicable if several rules are applicable. Conversely, this means that you must check whether several rules are applicable.

It is also important that you document this process appropriately so that a notified body or supervisory authority can check the classification based on your argumentation. According to Annex II of the MDR, these records must be included in the technical documentation. The wording requires:

f) the risk class of the device and the justification for the classification rule(s) applied in accordance with Annex VIII;

The justification for the applied rules is essentially based on the exclusion procedure – i.e. the justification for the fact that certain rules are not applicable. In addition, it should be comprehensible why which of the applicable definitions describe the respective device. In some cases, it is advisable to document why certain definitions do not apply.

Example of classification

In order to explain the classification to you using a simple example, let’s consider a device that everyone knows: A simple plaster. Let’s assume the following intended purpose:

The thinqbetter KLASSIK plaster is a textile wound dressing for the hygienic wound care of minor, superficial injuries to the skin. It covers the wound to protect it from contamination and does not stick to it. The application may take place for up to 14 days, as slower healing wounds should be treated by a specialist.

The following considerations on definitions from Article 2 now help:

“active device” does not apply;
“implantable device” does not apply;
“invasive device” does not apply;

We now recognize that the rules for invasive devices (5 to 8) as well as for active devices (9 to 13) cannot be applicable. This leaves the rules for non-invasive devices (1 to 4) and the special rules (14 to 22) for review.

However, we should first take a look at the definitions in Annex VIII:

“Transient” is not applicable as it describes a duration of use of less than 60 minutes;
“Short-term” is applicable. This definition allows an application between 60 minutes and 30 days.
“Long-term” is not applicable.

Further definitions relate to invasive and active devices and are therefore not to be considered in more detail.

In addition to the intended purpose, we also keep in mind that the device is non-invasive and is used temporarily.

Rule 1

All non-invasive devices are classified as class I, unless one of the rules set out hereinafter applies.

This rule is applicable to a temporarily applied non-invasive device.

The medical device is classified in class I according to rule 1.

Rule 2

All non-invasive devices intended for channelling or storing blood, body liquids, cells or tissues, liquids or gases for the purpose of eventual infusion, administration or introduction into the body are classified as class IIa:

if they may be connected to a class IIa, class IIb or class III active device; or
if they are intended for use for channelling or storing blood or other body liquids or for storing organs, parts of organs or body cells and tissues, except for blood bags; blood bags are classified as class IIb.

In all other cases, such devices are classified as class I.

The plaster is not intended for channeling or storing blood, other body fluids, cells or tissues, liquids or gases for the purpose of infusion, administration or introduction into the body. The rule is therefore not applicable.

Rule 3

All non-invasive devices intended for modifying the biological or chemical composition of human tissues or cells, blood, other body liquids or other liquids intended for implantation or administration into the body are classified as class IIb, unless the treatment for which the device is used consists of filtration, centrifugation or exchanges of gas, heat, in which case they are classified as class IIa.

All non-invasive devices consisting of a substance or a mixture of substances intended to be used in vitro in direct contact with human cells, tissues or organs taken from the human body or used in vitro with human embryos before their implantation or administration into the body are classified as class III.

The plaster is generally not used in the context or in connection with an implantation or administration of something into the body. The first part of the rule is therefore obviously not applicable. Since the plaster is also not used in the context of in vitro use, the second part does not need to be examined in more detail and is not applicable.

Rule 4

All non-invasive devices which come into contact with injured skin or mucous membrane are classified as:

class I if they are intended to be used as a mechanical barrier, for compression or for absorption of exudates;
class IIb if they are intended to be used principally for injuries to skin which have breached the dermis or mucous membrane and can only heal by secondary intent;
class IIa if they are principally intended to manage the micro-environment of injured skin or mucous membrane; and
class IIa in all other cases.

This rule applies also to the invasive devices that come into contact with injured mucous membrane.

The plaster comes into contact with injured skin as a wound dressing. Rule 4 is therefore applicable. Now it is necessary to examine in more detail which class results for the medical device from rule 4. For this purpose, the sub-items of the rule are checked.

Part 1 is applicable because a wound dressing is used as a mechanical barrier.

Part 2 is not applicable. Wounds for which a wound dressing is suitable are minor, superficial wounds that usually heal within a few days. In such wounds, there is no significant tissue loss and wound healing takes place within the framework of so-called primary wound healing. Large-area, deep abrasions heal via secondary wound healing. Here, granulation tissue is formed and the wound does not heal from the wound edges, but over a large area. In addition, significant scarring occurs here.

Part 3 is not applicable because the plaster is not used to influence the microenvironment of the wound.

Part 4 is not applicable because part 1 is applicable.

The medical device is classified in class I according to rule 4.

Rule 14 to 22

In order to keep the article clear, we will not go into rules 14 to 22. They are not applicable. In the short considerations shown above, you can see how the class for medical devices is determined. In order to create a record for the technical documentation, these considerations are documented in detail – including rules 14 to 22 of course.

Class of the medical device

In the current case, rules 1 and 4 are applicable. Both rules show that the medical device is classified in class I. However, if one of the rules requires a higher class, then this higher class would be the one that must be assigned to the device.

The thinqbetter KLASSIK plaster is a class I medical device.

MDR source

You can download the Medical Device Regulation (EU) 2017/745 here . Make sure you get the latest version, as corrections and consolidated versions are uploaded from time to time.