Classification of Medical Devices: MDR Classes and Rules

The classification of medical devices according to Regulation (EU) 2017/745 (MDR) represents one of the central elements of the entire regulatory pathway. The class assigned to the product determines the level of control required, the conformity assessment route, the technical documentation to be prepared, and the potential involvement of a Notified Body.

Classification is carried out through the application of the rules set out in Annex VIII MDR, which take into account factors such as intended use, invasiveness, duration of contact with the human body, use of energy, diagnostic or therapeutic purpose, and potential impact on the patient.

Correct classification therefore constitutes the starting point for establishing a coherent regulatory strategy, clinical activities, quality system, and document management throughout the entire life cycle of the medical device.

Definition of Medical Device and Regulatory Scope

Before determining the risk class of a product, it is necessary to verify whether it actually falls within the definition of a medical device provided by Regulation EU 2017/745 (MDR). Regulatory qualification is in fact the prerequisite for the entire certification process.

Regulatory Qualification of Medical Device

Article 2 of Regulation (EU) 2017/745 defines a medical device as any instrument, apparatus, software, implant, material, or other article intended by the manufacturer to be used on humans for specific medical purposes, such as diagnosis, prevention, monitoring, treatment, or alleviation of a disease or disability. Compared to the previous Directive 93/42/EEC, the MDR places greater emphasis on categories that are increasingly relevant today, such as medical software, digital applications, and remote monitoring systems.

An essential element of the definition concerns the principal mechanism of action of the product. For an article to be qualified as a medical device, its principal function must not be achieved by pharmacological, immunological, or metabolic means, even if such mechanisms may contribute to its action.

This aspect is particularly relevant for substance-based devices, where the boundary between medical device, medicinal product, or cosmetic may be complex to define. In such situations, the declared intended use and the clinical context of use become decisive.

Role of Intended Use

It is precisely the intended use that is the discriminating element for the qualification of a product as a medical device. It is in fact the purpose declared by the manufacturer, through labeling, instructions for use, or promotional material, that establishes whether a device falls within the scope of the MDR.

Intended use represents the starting point of the entire regulatory process: it not only distinguishes the medical device from other products but also forms the basis for assigning the risk class. Classification is in fact carried out by applying the rules of Annex VIII precisely according to the intended use and the inherent risks that such use entails for the patient or user.

Classification Criteria for Medical Devices According to MDR

The classification system provided by the MDR follows a risk-based approach. The objective is to apply regulatory requirements proportionate to the potential impact of the device on the safety of the patient, user, or third parties.

Classification does not depend on a single technical element, but on the combined analysis of various factors related to the intended use of the device. These include the level of invasiveness, the duration of contact with the human body, the use of energy, potential implantability, diagnostic or therapeutic purpose, and interaction with particularly critical organs or anatomical systems.

The main elements to be considered in determining the class of a medical device are therefore analyzed:

• Article 51 and Annex VIII of the Regulation, which constitute the basic regulatory reference;
• the role of the intended use provided by the manufacturer and the level of risk associated with a device;
• the concepts of invasiveness and contact with the human body, together with the duration of use of the device, aspects that significantly affect classification;
• the characteristics of implantable devices and active devices, which also include medical software;
• the twenty-two classification rules provided by Annex VIII, which allow the determination of the risk class applicable to each medical device.

Article 51 and Annex VIII as the Basis of Classification

Article 51 of the MDR establishes that medical devices are divided into classes I, IIa, IIb, and III based on the intended use and the associated level of risk.

The operational procedures for determining the class are instead defined in Annex VIII, which constitutes the main regulatory reference for classification. In addition to the 22 rules applicable to different types of devices, Annex VIII contains a series of general principles that guide its interpretation.

Among the most relevant principles are:

• Centrality of intended use: classification depends on the purpose intended by the manufacturer; any changes to the intended use require a reassessment of the risk class.
• Principle of maximum rigor: when more than one rule applies to a device, the one resulting in the highest risk class must be adopted.
• Separate classification of accessories and components: accessories and components are classified independently based on their function and associated risks.
• Software classification: software that controls or influences a device generally assumes the same class; independent software is instead classified according to Rule 11.
• Use in different anatomical sites: if the device is intended for multiple parts of the body, classification must consider the clinically most critical use.
• Continuous duration of use: duration must be assessed considering the intended continuous use, excluding brief interruptions due to maintenance, cleaning, or immediate replacement with an equivalent device.
• Direct diagnosis: a device is considered intended for direct diagnosis when it provides a diagnosis or information decisive for a clinical decision.

The MDCG 2021-24 guidance document provides particularly useful interpretative clarifications in more complex cases, supporting the manufacturer in identifying the most appropriate risk class for their device.

Intended Use and Risk Level

In the MDR system, classification is closely linked to the intended use provided by the manufacturer and the level of risk associated with the use of the device. Not only the product itself is considered, but the way it is used in clinical practice. Two technically similar devices may therefore fall into different classes if the following change:

• clinical purpose;
• context of use;
• level of impact on medical decisions or vital functions;
• degree of invasiveness;
• duration and type of contact with the patient.

Invasiveness and Contact with the Human Body

A central criterion in classification according to MDR concerns the level of invasiveness of the device and the type of interaction with the human body. Annex VIII and MDCG 2021-24 in fact attribute particular relevance to the way in which the device comes into contact with tissues, organs, or anatomical systems, since clinical risk increases progressively with the degree of penetration into the body.

According to the MDR, an invasive device is any device that penetrates, totally or partially, inside the body through a natural orifice or through the body surface.

The regulation also distinguishes surgically invasive devices, i.e., those introduced into the body through access created as part of a clinical or surgical procedure. This distinction is particularly important as it generally results in an increase in the applicable risk class.

The guidance clarifies that the concept of surgical procedure includes not only traditional surgical interventions, but also minimally invasive procedures in which the device artificially crosses the body surface. For this reason, needles, laparoscopic instruments, or catheters introduced through surgical access are considered surgically invasive devices.

For invasive devices, classification is mainly governed by rules 5, 6, 7, and 8 of Annex VIII. These rules consider the duration of use, the degree of invasiveness, the anatomical site involved, and the function performed by the device.

In general, the level of risk increases in relation to the permanence of the device in the human body and the possible consequences arising from a malfunction, especially when the device comes into contact with critical anatomical areas such as:

• central circulatory system;
• heart and great vessels;
• central nervous system;
• meninges and spinal cord.

Duration of Use: Transient, Short-Term, Long-Term

The concept of duration of use applies exclusively in the context of selecting the classification rule for invasive medical devices. This parameter is particularly relevant in classification since the risk associated with the device tends to increase with prolonged permanence or patient exposure.

Annex VIII distinguishes three categories of continuous duration:

• Transient: use for less than 60 minutes.
• Short-term: use between 60 minutes and 30 days.
• Long-term: use for more than 30 days.

MDCG 2021-24 clarifies a fundamental principle in assessing the duration of use of medical devices: what matters is not the material time of application, but the duration of the effect exerted within the body. In other words, even a device applied in a few seconds—such as a topical cream—can result in a much longer duration of use, if its components remain in the tissues or continue to exert a clinical action over time.

This approach is particularly relevant for product categories such as absorbable substances, active coatings, resorbable implantable devices, and sustained-release systems, for which regulatory assessment must consider the actual persistence and activity of the device in the human body.

Duration of use also directly affects the biological evaluation of the device. Longer exposure may increase the risk of toxicity, inflammation, infection, material degradation, and mechanical or functional alterations. For this reason, the MDR generally requires more robust evidence and more thorough controls for devices intended to remain in the body for prolonged periods.

The combination of duration of use and invasiveness also represents one of the most decisive elements in final classification. A surgically invasive device used transiently may fall into a relatively contained class, while the same device, if intended to remain for more than thirty days, may be automatically classified in a higher class.

Implantable Devices

The MDR attaches particular importance to implantable devices, in consideration of the specific risks associated with their permanence within the body and their direct contact with tissues, organs, or body fluids. An implantable device means any device, including absorbable ones, intended to be introduced totally into the human body or to replace an epithelial surface or the surface of the eye by means of clinical intervention and intended to remain in place after the procedure. The definition also includes devices intended to be introduced partially into the human body by means of clinical intervention and to remain in place for at least thirty days.

The concept of procedure must be interpreted restrictively and includes exclusively the clinical implantation procedure and the immediately connected post-operative care. It does not therefore coincide with the entire duration of therapeutic treatment or the period necessary to achieve the clinical objective. It follows that the permanence of the device must be assessed with reference to the time elapsed after implantation and not to the overall duration of the pathology or therapy.

This interpretation is particularly relevant for devices that, although not intended to remain indefinitely in the body, remain in place for a period exceeding thirty days. In these cases, the device must be considered implantable even if subsequent programmed removal is planned. This is the case, for example, of orthopedic plates, bone screws, intramedullary nails, and other fixation systems used in the treatment of fractures: such devices retain their nature as implants even when explantation is performed after bone consolidation. According to the clarification provided by the MDCG, implantation and subsequent removal are in fact two distinct and autonomous clinical procedures.

Furthermore, some devices only partially introduced into the body may still be qualified as implantable. A significant example is represented by implantable venous ports for infusion, inserted through a dedicated procedure and designed to remain in place for prolonged periods exceeding thirty days. Conversely, devices intended for temporary use and limited permanence do not fall within the definition of implantable device. Among these are non-tunneled central venous catheters, generally used for short-term vascular access and removed after a few days, as well as non-absorbable sutures intended to be removed before thirty days from application.

Rule 8 of Annex VIII is the main reference for implantable devices. This rule attributes particular relevance to the anatomical site of implantation, the degree of invasiveness, contact with vital organs or the central nervous system, and the function performed by the device. In general, the level of risk increases in relation to the prolonged permanence of the device in the human body and the possibility that a malfunction may result in serious or irreversible consequences for the patient.

Active Devices

Active devices represent a relevant category in the MDR, since their operation depends on an external energy source other than that generated directly by the human body or by gravity. A device is defined as active when its operation requires an external energy source and when that energy is transformed or modified to achieve the intended use provided by the manufacturer.

The distinctive element therefore does not lie in the simple presence of energy, but in its conversion or processing by the device. This principle makes it possible to distinguish devices that, although appearing similar from a functional point of view, have a different regulatory classification. For example, electrodes used for the acquisition of electrocardiographic (ECG) or electroencephalographic (EEG) signals are not generally considered active devices, since they merely transmit biological signals without significantly modifying their energy. Conversely, electrodes used in electrosurgery are active devices as they convert electrical energy into thermal energy intended to produce a biological effect on tissues.

It is important to emphasize that not all energy sources automatically determine qualification as an active device. Manual instruments such as syringes, surgical forceps, or traditional scalpels do not fall into this category, since their energy derives directly from the operator. Devices that accumulate, store, or release energy autonomously are instead considered active, such as some preloaded spring systems, mechanical pumps, or devices that use batteries, electrical energy, pneumatic sources, or other forms of external power.

Active devices include numerous technologies used in modern clinical practice, such as ventilators, infusion pumps, physiological monitoring systems, radiological equipment, and laser therapy devices.

The classification rules applicable to active devices are mainly contained in rules 9 to 13 of Annex VIII. These rules attribute particular relevance to the nature of the energy administered or exchanged with the patient, the anatomical part involved, the clinical purpose, and the possible consequences arising from a device malfunction. In general, the level of risk increases when the device is intended to support or maintain vital functions, to administer potentially dangerous energy, or to provide clinical information that may influence critical therapeutic decisions.

Medical Software

Software is also considered an active device under the MDR and its classification is mainly governed by Rule 11 of Annex VIII.

The qualification of medical software is further clarified by the MDCG 2019-11 guidance document, which distinguishes between software that achieves clinical purposes and software that merely controls or influences the operation of a medical device. In the first case, the software may be qualified as a medical device and, if it falls within the scope of the MDR, is subject to independent classification: it is therefore configured as Medical Device Software (MDSW); in the second case, however, it is not classified independently and follows the class of the device to which it is connected, according to the rules of Annex VIII.

The same guidance provides interpretative criteria for establishing whether software falls within the scope of the MDR and, consequently, for determining its risk class. In particular, Rule 11 assigns the class according to the role of the software in the clinical decision-making process and the impact that the processed information may have on patient health. For example, software that provides information used for diagnostic or therapeutic decisions potentially associated with serious or irreversible consequences is generally classified in higher classes, while software intended for monitoring physiological parameters tends to fall into lower classes, unless it concerns critical conditions.

Finally, technological development has led to the spread of hybrid devices that integrate software, active components, and/or implantable systems. In these cases, classification requires a careful analysis of the clinical functions and risks associated with each element of the system.

Classification Rules

To complete the framework described so far, a summary of the twenty-two rules defined by Annex VIII is provided below, which represent the basis for assigning the risk class of medical devices.

Medical Device Classes

The MDR divides devices into four main classes, associated with increasing levels of regulatory control. To these are added classes Is (sterile devices), Ir (reusable devices), and Im (devices with a measuring function).

Class I and Subclasses Ir, Is, Im

Class I generally includes non-invasive devices characterized by a limited risk profile for the patient. Among the most common examples are manual wheelchairs, hospital beds, stethoscopes, bandages, and non-sterile dressings.

Within class I, the MDR provides for some subclasses that require additional verification on specific aspects of the device:

• Class Is: includes devices supplied sterile, for which the Notified Body (NB) verifies aspects related to the sterilization process. Examples: sterile surgical gloves, sterile gauze, and sterile single-use kits.
• Class Im: includes devices that perform measurements and for which accuracy, precision, and metrological reliability must be demonstrated. Examples: medical thermometers, sphygmomanometers, medical scales, and blood glucose measurement devices.
• Class Ir: includes instruments intended to be reused after appropriate cleaning, disinfection, and, where necessary, sterilization processes. Examples: surgical forceps, surgical scissors, and other reusable surgical instruments.

Class IIa

Class IIa includes devices with moderate risk, often intended for diagnosis, monitoring, or therapeutic support. For these products, the involvement of a Notified Body in conformity assessment is mandatory.

Among the most frequent examples are:

• certain types of active devices for diagnostic purposes, such as ultrasound diagnostic equipment, and therapeutic purposes, such as muscle stimulation devices;
• certain categories of surgically invasive devices, including needles, syringes, and infusion cannulas;
• medical software that supports diagnostic or therapeutic decisions, provided that an error cannot result in the death of the patient or an irreversible deterioration of their health status;
• software intended for monitoring non-vital physiological parameters.

Class IIb

Class IIb devices have a higher risk profile and include technologies that can significantly affect the patient’s clinical condition.

Among the most common examples:

• ventilators;
• infusion pumps;
• equipment that emits ionizing radiation and is intended for radiology;
• certain types of long-term implants;
• medical software intended for monitoring vital physiological parameters or supporting diagnostic and therapeutic decisions whose error could result in serious deterioration of the patient’s health status.

For such devices, the level of technical and clinical depth required increases significantly.

Class III

Class III represents the maximum level provided by the MDR. This category includes devices:

• in contact with the heart, central circulatory system, or central nervous system;
• containing substances absorbable by the human body;
• critical implantable devices, such as cardiac valve prostheses;
• intended for life support, such as ventricular assist devices.

For these products, a particularly robust clinical evaluation is normally required and, in most cases, a dedicated clinical investigation.

Intervention of the Competent Authority in Case of Dispute on Class

Should interpretative doubts or disagreements arise regarding the application of the classification rules provided by Annex VIII MDR, the national competent authority may intervene to define the correct classification of the device.

In Italy, this function is performed by the Ministry of Health, which may request documentary clarifications, review the classification proposed by the manufacturer, or adopt specific regulatory decisions.

When Self-Declaration by the Manufacturer Is Permitted

Before exploring the topic in depth, a clarification is appropriate: the expression self-declaration by the manufacturer is commonly used in the sector, but is not technically correct. It refers to the possibility, provided by the MDR, for the manufacturer to complete the conformity assessment procedure without the involvement of a Notified Body.

This possibility is limited to class I medical devices that are not sterile, do not have a measuring function, and are not composed of reusable surgical instruments. In such cases, the manufacturer may independently assess the conformity of the device with the applicable requirements of the MDR, draw up the EU declaration of conformity, and affix the CE marking without having to obtain a certificate issued by an NB.

It should be noted that the competent authority may, however, carry out documentary checks or sample inspections after placing on the market. In Italy, such activities are carried out by the Ministry of Health as part of market surveillance and vigilance activities.

When the Notified Body Intervenes

For class IIa, IIb, and III medical devices, the involvement of a Notified Body is mandatory. However, a clarification is necessary for subclasses Is, Im, and Ir. In these cases, the intervention of the NB is formally limited to the specific aspects that justify the classification (sterility, measuring function, or reusability). In practice, however, the difficulty in determining the boundary between the elements subject to NB assessment and the remaining content of the technical documentation often makes the assessment process comparable to that provided for higher risk classes.

The role of the NB is to verify that the device and the related quality management system meet the applicable requirements of the MDR before placing on the market.

Conformity assessment involves the analysis of the technical documentation of the device and the quality system implemented by the manufacturer. During the documentary review, the NB may request clarifications or additional evidence and issue any non-conformities that must be adequately managed and closed by the manufacturer.

Once the documentation assessment phase has been successfully completed, quality system audits are carried out and, subsequently, the CE certificate is issued.

However, the intervention of the NB does not end with initial certification. The MDR in fact provides for continuous surveillance through periodic audits, reviews of technical documentation, and verification of post-market surveillance (PMS) and post-market clinical follow-up (PMCF) activities, in order to ensure the maintenance of conformity throughout the entire life cycle of the device.

Declaration of Conformity, CE Certificate, and CE Marking

Once the conformity assessment has been successfully completed, the manufacturer can complete the regulatory pathway necessary for the commercialization of the device.

In the case of devices subject to NB intervention, the process first involves the issuance of the CE certificate. Subsequently, the manufacturer draws up the declaration of conformity, a document with which it formally assumes responsibility for the conformity of the device with the applicable MDR requirements.

Before placing the device on the European Union market, the manufacturer must ensure that it has affixed the CE marking. Through it, the manufacturer declares that the device:

• meets the applicable requirements of the MDR;
• is supported by adequate technical and clinical evidence;
• has a compliant PMS system;
• has been subjected to the assessment procedures provided for its risk class.

For devices subject to certification by the NB, the CE marking must be accompanied by the identification number of the body involved in the assessment.

Documentation and Evidence Required Based on Class

The MDR requires the preparation of technical documentation (or technical file) in accordance with Annexes II and III, regardless of the class of the device. It follows that the documentary obligation is transversal and does not vary according to classification: the structure of the technical file and classification remain formally independent.

However, for devices belonging to classes higher than class I, the involvement of the NB entails, in practice, greater attention and an in-depth examination of specific technical, clinical, and regulatory aspects by the manufacturer. This indirectly results in an increase in the level of evidence required to demonstrate conformity.

Technical documentation generally includes:

• description of the device and intended use;
• classification and regulatory rationale;
• general safety and performance requirements (GSPR);
• risk management;
• verification and validation;
• preclinical and clinical data;
• labeling and instructions for use;
• PMS and PMCF activities.

Classification therefore mainly affects the level of detail and depth of evidence required.

Conclusion

Classification according to the MDR therefore represents the starting point for building the entire regulatory pathway of the medical device. Correct interpretation and application of the classification rules, followed by a coherent assignment of the risk class to one’s medical device, make it possible to define from the outset the documentary requirements, clinical strategy, certification activities, and post-market obligations. For this reason, it is essential to approach MDR classification through a structured technical and regulatory analysis.