What UDI-DI Identifies
MDR Article 27(1) and IVDR Article 24(1)define the UDI-DI in near-identical terms: "a UDI device identifier ('UDI-DI') specific to a manufacturer and a device, providing access to the information laid down in Part B of Annex VI." It is a fixed code for one device model, version, and configuration, issued by one of the four Commission-recognized issuing entities (GS1, HIBCC, ICCBBA, or IFA).
The UDI-DI is what goes on the physical label and the packaging, and it is what EUDAMED uses as the anchor for a device registration record. Two physical units from the same production run carry the same UDI-DI; a device with a different model number, a different sterility status, or a different pack quantity gets a different one.
What Basic UDI-DI Identifies
MDR Annex VI Part Cdefines the Basic UDI-DI as "the primary identifier of a device model. It is the DI assigned at the level of the device unit of use. It is the main key for records in the UDI database and is referenced in relevant certificates and EU declarations of conformity." IVDR sets out its own, parallel Annex VI, Part C for the same purpose.
MDCG 2018-1 Rev.4, the Commission's guidance on the Basic UDI-DI, sharpens what that means in practice: it is "the main key in the database and relevant documentation (e.g. certificates, declaration of conformity, technical documentation and summary of safety and clinical performance) to connect devices with same intended purpose, risk class and essential design and manufacturing characteristics." The same guidance states it is "independent/separate from the packaging/labelling of the device and it does not appear on any trade item."
MDCG 2018-1 Rev.4 and its companion Q&A, MDCG 2022-7, both address the UDI system of what they call "the two medical device Regulations," meaning MDR and IVDR together, so this definition and the relationship rule below hold under both.
The Difference at a Glance
| UDI-DI | Basic UDI-DI | |
|---|---|---|
| Identifies | One specific device model, version, and configuration | A group of devices sharing intended purpose, risk class, and essential design and manufacturing characteristics |
| Legal basis | MDR Article 27(1) / IVDR Article 24(1) | MDR Annex VI Part C (and IVDR's own Annex VI, Part C) |
| Appears on | Device label, packaging, EUDAMED device record | EU Declaration of Conformity, certificates, technical documentation, SSCP, EUDAMED record. Never the label. |
| Assigned by | Manufacturer, via a UDI issuing entity | Manufacturer |
| Relationship | Each UDI-DI links to exactly one Basic UDI-DI (MDCG 2018-1 Rev.4) | One Basic UDI-DI can cover multiple UDI-DIs |
Worked Examples
The definitions above are abstract until they meet an actual product line. Two examples, one built from the trigger list in MDCG 2018-1 Rev.4 and one taken directly from an MDCG Q&A, show how the two identifiers move independently of each other.
Example 1: The same device in two pack sizes
MDCG 2022-7 answers this one directly: "where the number of devices in a package changes e.g. from 5 to 10, a new UDI-DI assignment to the package would be required," because the guidance treats a pack-quantity change as a misidentification risk under MDR Annex VI Part C Section 3.9. So a 5-pack and a 10-pack of the same instrument need two separate UDI-DIs. Nothing about intended purpose, risk class, or essential design and manufacturing characteristics changed between them, so under the Basic UDI-DI definition above, both UDI-DIs can be grouped under one Basic UDI-DI.
Example 2: Two components sold only as a pair
MDCG 2022-7 works through a device made of two physically separate modules, one patient-facing and one physician-facing, connected over a network, that only function together and are only ever sold as a set. The guidance's answer: "given the components can only be used together and sold in this combination, they could be assigned the same Basic UDI-DI." The grouping question turns on whether the components are placed on the market, used, and regulated as one device, not on how many physical boxes ship.
Where Each One Appears
Two further points from MDCG 2022-7 are worth knowing before setting up a UDI structure for a portfolio. First, the check digit is an integral part of the Basic UDI-DI: the guidance states that "without the check digit, the Basic UDI-DI would be incomplete," and the complete form, check digit included, is what has to reach EUDAMED and appear on the Declaration of Conformity. Second, the relationship between a Basic UDI-DI and a Declaration of Conformity is not one-to-one in the other direction: a single Declaration of Conformity may reference more than one Basic UDI-DI, and the same Basic UDI-DI can be referenced in more than one Declaration of Conformity.
Common Confusions
| Confusion | What Is Actually True |
|---|---|
| "A UDI-DI change always means a new Basic UDI-DI too" | Not necessarily. The two identifiers respond to different triggers: a UDI-DI changes on an Annex VI Part C data-element change, a Basic UDI-DI changes only if intended purpose, risk class, or essential design and manufacturing characteristics change. See UDI-DI Grouping Rules for the full UDI-DI trigger list. |
| "The Basic UDI-DI is just a shorter version of the UDI-DI" | No, they are structurally unrelated identifiers issued for different purposes. One is not derived from or abbreviated from the other. |
| "Whoever puts their brand on the box can request their own Basic UDI-DI" | Assignment stays with the manufacturer identified on the label, private-label and distributor arrangements included. See Who Can Assign a UDI-DI? Manufacturer vs. Distributor for the MDCG 2026-5 position. |
Relevant Guidance
| Document | Topic | Key Content Used Here |
|---|---|---|
| MDCG 2018-1 Rev.4 (April 2021) | Guidance on Basic UDI-DI and changes to UDI-DI | Basic UDI-DI definition, the one-Basic-UDI-DI-per-UDI-DI rule, the UDI-DI change trigger list |
| MDCG 2022-7 (May 2022) | Questions and answers on the UDI system under MDR and IVDR | The pack-quantity and linked-components worked examples, the check digit rule, the Declaration of Conformity multiplicity rule |
| MDR Annex VI Part C | Regulatory text for the UDI system | Statutory Basic UDI-DI definition |
| MDR Article 27(1) / IVDR Article 24(1) | Legal basis for the UDI system under MDR and IVDR respectively | Statutory UDI-DI definition |
UDI-DI and Basic UDI-DI answer two different questions: which exact device is this, and which regulatory file does it belong to. Getting that distinction right before a EUDAMED submission avoids both a labeling error, printing something that should never appear on packaging, and a documentation error, scattering one device family across records that should be linked. Neither identifier is optional, and neither substitutes for the other.
Frequently Asked Questions
What is the actual difference between a Basic UDI-DI and a UDI-DI?
The UDI-DI identifies one specific device model, version, and configuration; it goes on the label and changes whenever the device's identity or essential characteristics change. The Basic UDI-DI is a grouping identifier for devices sharing the same intended purpose, risk class, and essential design and manufacturing characteristics; it never appears on the label and instead sits in the Declaration of Conformity, certificates, technical documentation, and the EUDAMED record.
Can two different UDI-DIs share the same Basic UDI-DI?
Yes. MDCG 2018-1 Rev.4 defines the Basic UDI-DI as the key connecting devices with the same intended purpose, risk class, and essential design and manufacturing characteristics, so multiple UDI-DI variants of what is regulatorily the same device, such as different pack sizes, can share one Basic UDI-DI.
Can one UDI-DI be linked to more than one Basic UDI-DI?
No. MDCG 2018-1 Rev.4 states plainly that a UDI-DI shall be associated with one and only one Basic UDI-DI. The relationship only runs one way: one Basic UDI-DI can cover many UDI-DIs, but each UDI-DI belongs to exactly one Basic UDI-DI.
Does the Basic UDI-DI ever appear on the device label or packaging?
No. MDCG 2018-1 Rev.4 describes it as independent and separate from the packaging and labelling of the device, and states it does not appear on any trade item. It belongs in regulatory documentation and the EUDAMED record only.
Can one Declaration of Conformity reference more than one Basic UDI-DI?
Yes. MDCG 2022-7 confirms a Declaration of Conformity may reference more than one Basic UDI-DI, and the same Basic UDI-DI can be referenced in more than one Declaration of Conformity.
Does IVDR use the same Basic UDI-DI and UDI-DI distinction as MDR?
Yes. MDCG 2018-1 Rev.4 and MDCG 2022-7 both state that they interpret the UDI provisions of what the guidance calls "the two medical device Regulations," and IVDR sets out its own Annex VI, Part C and Article 24 UDI system in parallel with MDR's. The definitions and the one-to-many relationship described above apply under both regulations.