Written and maintained by CASRAI Editorial Board
Last updated
General regulatory information for lab, clinic and supply staff; it is not legal, regulatory or medical advice.
Short answer
A UDI-PI is the production identifier: the conditional, variable part of a US Unique Device Identifier (UDI). It can carry the lot or batch, serial number, expiration date, manufacture date, or an HCT/P identification code. The UDI-DI (device identifier) is the other part: the mandatory, fixed portion that identifies the labeler and the specific version or model of the device.
Definition and scope
Under the FDA’s UDI rule, 21 CFR 830.3 defines a UDI as an identifier that adequately identifies a device through its distribution and use. It is composed of two parts. The FDA’s UDI Basics page gives the same two-part description: a UDI “generally consists of” a device identifier (DI) and a production identifier (PI). This page covers the US rule; other jurisdictions use their own terminology and are not described here.
People search the same pair of ideas under several names. “UDI DI” and “UDI device identifier” mean the fixed part; “UDI production identifier” and “UDI PI” mean the variable part. For the full UDI picture see UDI for medical devices; for how a DI record is created, see UDI labeling and GUDID submission.
What is the difference between UDI-DI and UDI-PI?
The DI is fixed and always required; the PI is variable and only appears when it applies. 21 CFR 830.3 calls the DI “a mandatory, fixed portion of a UDI” and the PI “a conditional, variable portion of a UDI”, and the second is described as identifying its elements “when included on the label of the device”.
| Feature | UDI-DI (device identifier) | UDI-PI (production identifier) |
|---|---|---|
| Status in the rule | Mandatory | Conditional |
| Nature | Fixed | Variable |
| What it identifies | The labeler and the specific version or model of the device | One or more of: lot or batch, serial number, expiration date, manufacture date, HCT/P identification code |
Source: 21 CFR 830.3 (checked 2026-10-31).
What goes in a production identifier?
The rule lists five possible elements. A given label may carry some, all or none of them, because the PI is conditional.
| PI element | What 21 CFR 830.3 says it identifies |
|---|---|
| Lot or batch | The lot or batch within which a device was manufactured |
| Serial number | The serial number of a specific device |
| Expiration date | The expiration date of a specific device |
| Manufacture date | The date a specific device was manufactured |
| HCT/P code | For a human cell, tissue, or cellular or tissue-based product regulated as a device, the distinct identification code required by 21 CFR 1271.290(c) |
Source: 21 CFR 830.3 and FDA UDI Basics (checked 2026-10-31). The FDA also states that labelers must present the UDI in plain-text and in machine-readable (AIDC) form, and that dates on labels and packages must use the YYYY-MM-DD format. To read one of these dates on a physical label, see the date of manufacture symbol; for the barcode that often carries the data, see GS1-128 barcodes.
Does the UDI-PI change with each lot?
By definition, the PI is the variable portion of the UDI, and the lot or batch is one of the things it can identify. So when a label’s PI includes a lot or batch, that element reflects the lot the device was made in and can differ from one lot to the next. The regulation does not phrase it as “changes with each lot”; this is the reading that follows from the definition. A PI containing only a serial number would identify a specific device instead.
The rule defines a lot or batch as one finished device or more of a single type, model, class, size, composition or software version, “manufactured under essentially the same conditions” and “intended to have uniform characteristics and quality within specified limits”. For how lot numbers are read in practice, see lot numbers and how to read a lot number.
What changes the DI, and what only changes the PI
This is the distinction many short glossary entries blur. 21 CFR 830.50 lists exactly two situations that require a new DI:
| Event | Effect under the rule |
|---|---|
| A change to a device that is required to bear a UDI results in a new version or model | A new DI must be assigned to the new version or model (830.50(a)) |
| A new device package is created | A new DI must be assigned to the new package (830.50(b)) |
| A different lot, serial number, expiration date or manufacture date | These are PI elements as defined in 830.3; 830.50 does not list them as triggers for a new DI |
Sources: 21 CFR 830.50 and 830.3 (checked 2026-10-31). Section 830.50 lists only the two triggers above.
Where it matters for labs and clinics
Because the two parts answer different questions, a label can be read in two passes. The DI part answers “which labeler and which version or model or package is this?” The PI part, where present, answers “which lot, which unit, and which dates?” This follows directly from the definitions above and does not depend on any one vendor’s system. Records that need to separate the model from the production data can follow the same split. The FDA’s UDI Basics page describes the DI as identifying the labeler and the specific version or model, and the PI as the part that varies with production.
Common misunderstandings
- “The UDI is the barcode.” The UDI is the identifier; the plain-text and machine-readable forms are how the labeler presents it (FDA UDI Basics).
- “Every UDI has a lot and expiration date.” The PI is conditional and identifies its elements only “when included on the label” (21 CFR 830.3).
- “A new lot gets a new DI.” The rule’s listed triggers for a new DI are a new version or model and a new device package (21 CFR 830.50), not a new lot.
- “UDI-DI is the same as the lot number.” The lot or batch is a possible PI element, not part of the DI.
FAQ
What is the difference between UDI-DI and UDI-PI?
The DI is the mandatory, fixed part that identifies the labeler and the version or model; the PI is the conditional, variable part that can identify lot or batch, serial number, expiration date, manufacture date, or an HCT/P code.
What goes in a production identifier?
Any of five elements when included on the label: lot or batch, serial number, expiration date, manufacture date, and, for certain HCT/Ps regulated as devices, the code required by 21 CFR 1271.290(c).
Does the UDI-PI change with each lot?
The PI is the variable portion and may include the lot or batch, so that element can differ between lots. The DI is not listed as changing with a new lot; 21 CFR 830.50 names a new version or model and a new package as the triggers for a new DI.
What is a UDI device identifier?
It is another name for the DI, the fixed portion of the UDI that identifies the labeler and the specific version or model of the device.
Sources
All sources checked 2026-10-31.
- 21 CFR 830.3, Definitions: https://www.law.cornell.edu/cfr/text/21/830.3
- 21 CFR 830.50, Changes that require use of a new device identifier: https://www.law.cornell.edu/cfr/text/21/830.50
- FDA, UDI Basics: https://www.fda.gov/medical-devices/unique-device-identification-system-udi-system/udi-basics
