MDR Classification Rules: A Plain-Language Guide to All 22 Rules

Your device’s class determines the conformity assessment route, whether you need a notified body, how much clinical evidence is required and your post-market obligations. Misclassification can force a months-long submission to start over.

This guide explains the classification logic of EU MDR 2017/745 Annex VIII in plain language. For a quick preliminary assessment, try our free MDR classification tool.

The four risk classes

Class I includes three sub-groups: sterile devices (Is), devices with a measuring function (Im) and reusable surgical instruments (Ir). For these, the notified body only assesses the aspects related to sterility, metrology or reprocessing.

What determines the class

Classification always starts from the intended purpose declared by the manufacturer on the label and instructions for use, not from technical features alone. Other key criteria:

• Duration: transient (under 60 minutes), short-term (60 minutes to 30 days) or long-term (over 30 days)
• Invasiveness: non-invasive, invasive via body orifice, surgically invasive or implantable
• Anatomical site: especially direct contact with the heart, central circulatory system or central nervous system
• Active or not: whether the device depends on an energy source
• Composition: medicinal substances, human or animal tissues, nanomaterials or absorbed substances

The 22 rules at a glance

Non-invasive devices (Rules 1–4)

• Rule 1: All non-invasive devices not covered elsewhere are Class I.
• Rule 2: Devices for channelling or storing blood, body liquids, cells or tissues for administration are Class IIa; blood bags are Class IIb.
• Rule 3: Devices modifying the biological or chemical composition of blood or body liquids are Class IIb; those using only filtration, centrifugation or gas/heat exchange are Class IIa. Substances used in vitro in direct contact with human cells or embryos (e.g. IVF media) are Class III.
• Rule 4: Devices contacting injured skin are Class I as mechanical barriers, Class IIa when managing the micro-environment and Class IIb for wounds breaching the dermis that heal by secondary intent.

Invasive devices (Rules 5–8)

• Rule 5: Devices entering body orifices are Class I, IIa or IIb depending on duration, one class lower in the oral cavity, ear canal or nasal cavity.
• Rule 6: Transient surgically invasive devices are Class IIa; reusable surgical instruments are Class I; those in direct contact with the heart, central circulatory system or CNS are Class III.
• Rule 7: Short-term surgically invasive devices are Class IIa; Class III if they have a biological effect, are absorbed or directly contact the heart, central circulation or CNS.
• Rule 8: Implantable and long-term surgically invasive devices are Class IIb; Class IIa if placed in teeth; Class III for devices contacting the heart, central circulation or CNS, absorbable devices, drug-delivering devices, active implants, breast implants, surgical meshes, total or partial joint replacements and implants contacting the spinal column.

Note for orthopaedic manufacturers: Ancillary components of joint replacements (screws, wedges, plates) and of spinal implants (screws, hooks, plates) are excluded from the Rule 8 Class III provisions and typically remain Class IIb.

Active devices (Rules 9–13)

• Rule 9: Active therapeutic devices are Class IIa; Class IIb if delivering energy in a potentially hazardous way; Class III if controlling active implants.
• Rule 10: Active diagnostic and monitoring devices are generally Class IIa; Class IIb when monitoring vital parameters where variations could cause immediate danger, or emitting ionising radiation for diagnostic radiology.
• Rule 11: Software providing information for diagnostic or therapeutic decisions is at least Class IIa; Class IIb if decisions could cause serious deterioration or surgical intervention; Class III if they could cause death or irreversible deterioration.
• Rule 12: Active devices administering or removing medicines or body substances are Class IIa, or IIb if hazardous.
• Rule 13: All other active devices are Class I.

Special rules (Rules 14–22)

These apply regardless of device type and usually raise the class: medicinal substances with ancillary action (Rule 14, Class III), contraception (Rule 15), disinfection and sterilisation devices (Rule 16), X-ray image recording (Rule 17), tissues and cells (Rule 18, Class III), nanomaterials (Rule 19), inhalers (Rule 20), devices made of absorbed substances (Rule 21) and active therapeutic devices with integrated diagnostics (Rule 22, Class III).

Implementing rules that are often missed

1. The strictest rule wins when several apply (3.5).
2. Accessories are classified in their own right (3.2).
3. Software driving a device takes the device’s class; standalone software is classified on its own (3.3).
4. Duration means continuous use, including immediate replacement with an identical device (3.6).
5. “Direct contact with the heart” requires the device to be specifically intended for that purpose; incidental contact is not enough.

Documenting your classification

Your technical documentation should contain a short but reasoned classification section: intended purpose, duration, invasiveness and anatomical site, all rules considered and why they do or do not apply, and the resulting class and conformity route. The European Commission’s MDCG 2021-24 guidance contains examples for every rule and is the reference notified bodies use.

Run a preliminary check with our MDR classification tool, or see our CE/MDR service for a justified classification report.

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