Contains Nonbinding Recommendations
Unique Device Identification System: 
Form and Content of the Unique 
Device Identifier (UDI) 
Guidance for Industry and 
Food and Drug Administration Staff 
Document issued on July 7, 2021. 
The draft of this document was issued on July 25, 2016.
For questions about this document regarding CDRH-regulated devices, UDI Regulatory Policy 
Support, 301-796-5995, email: GUDIDSupport@fda.hhs.gov. For questions about this document 
regarding CBER-regulated devices, contact the Office of Communication, Outreach, and 
Development (OCOD) at 1-800-835-4709 or 240-402-8010, or by email at ocod@fda.hhs.gov.
    
U.S. Department of Health and Human Services
Food and Drug Administration
Center for Devices and Radiological Health
Center for Biologics Evaluation and Research Contains Nonbinding Recommendations
Preface
Public Comment
You may submit electronic comments and suggestions at any time for Agency consideration to 
https://www.regulations.gov. Submit written comments to the Dockets Management Staff, Food 
and Drug Administration, 5630 Fishers Lane, Room 1061, (HFA-305), Rockville, MD 20852.  
Identify all comments with the docket number FDA-2016-D-1853. Comments may not be acted 
upon by the Agency until the document is next revised or updated.
Additional Copies
CDRH
Additional copies are available from the Internet. You may also send an email request to
CDRH-Guidance@fda.hhs.gov to receive a copy of the guidance. Please include the document 
number 1500035 and complete title of the guidance in the request.
CBER
Additional copies are available from the Center for Biologics Evaluation and Research (CBER), 
Office of Communication, Outreach, and Development (OCOD), 10903 New Hampshire Ave., 
WO71, Room 3128, Silver Spring, MD 20903, or by calling 1-800-835-4709 or 240-402-8010, 
by email, ocod@fda.hhs.gov, or from the Internet at 
https://www.fda.gov/vaccines-blood-biologics/guidance-compliance-regulatory-information-
biologics/biologics-guidances.  Contains Nonbinding Recommendations
Table of Contents
I.  Introduction ............................................................................................................................. 1
II.  Background ............................................................................................................................. 2
III.  Scope .................................................................................................................................... 2
IV.  Unique Device Identifier (UDI) ........................................................................................... 3
A.  Forms of UDI ................................................................................................................... 4
1.  Easily readable plain-text ............................................................................................. 4
2.  AIDC ............................................................................................................................ 5
B.  Content of UDI ................................................................................................................. 6
C.  Data delimiters ................................................................................................................. 7
D.  Order of the data represented in the easily readable plain-text form of UDI carrier ....... 8
E.  Stand-Alone Software ...................................................................................................... 8 Contains Nonbinding Recommendations
Unique Device Identification System: 
Form and Content of the Unique 
Device Identifier (UDI)
Guidance for Industry and
Food and Drug Administration Staff
This guidance represents the current thinking of the Food and Drug Administration (FDA 
or Agency) on this topic. It does not establish any rights for any person and is not binding 
on FDA or the public. You can use an alternative approach if it satisfies the requirements 
of the applicable statutes and regulations. To discuss an alternative approach, contact the 
FDA staff or Office responsible for this guidance as listed on the title page. 
I.  Introduction
This document is intended to assist labelers1 and FDA-accredited issuing agencies2 in 
complying with unique device identifier (UDI) labeling requirements, including by clarifying 
FDAs interpretation of certain requirements under 21 CFR 801.40. Specifically, this 
guidance describes the requirements for and FDAs recommendations regarding the form and 
content of the UDI to help ensure that the UDIs developed under systems for the issuance of 
UDIs meet the objectives of the Unique Device Identification System Final Rule, 78 FR 
58786 (September 24, 2013) (UDI Rule).3
Throughout this guidance document, the terms we, us, and our refer to FDA staff from 
Center for Devices and Radiological Health (CDRH) and the Center for Biologics Evaluation 
and Research (CBER).
1 Labeler is defined at 21 CFR 801.3 as (1) any person who causes a label to be applied to a device with the 
intent that the device will be commercially distributed without any intended subsequent replacement or 
modification of the label; and (2) any person who causes the label of a device to be replaced or modified with 
the intent that the device will be commercially distributed without any subsequent replacement or modification 
of the label, except that the addition of the name of, and contact information for, a person who distributes the 
device, without making any other changes to the label, is not a modification for the purposes of determining 
whether a person is a labeler. 
2 Issuing agency is defined at 21 CFR 830.3 as an organization accredited by FDA to operate a system for the 
issuance of unique device identifiers.
3 Available at: https://www.federalregister.gov/articles/2013/09/24/2013-23059/unique-device-identification-
system. 
1 Contains Nonbinding Recommendations
The contents of this document do not have the force and effect of law and are not meant to 
bind the public in any way, unless specifically incorporated into a contract. This document is 
intended only to provide clarity to the public regarding existing requirements under the law. 
FDA guidance documents, including this guidance, should be viewed only as 
recommendations, unless specific regulatory or statutory requirements are cited. The use of 
the word should in Agency guidance means that something is suggested or recommended, 
but not required.
II.  Background
The UDI Rule requires the label and device package4 of every medical device to bear a 
UDI, unless an exception or alternative applies (21 CFR 801.20). Additionally, some 
devices are required to bear a permanent marking providing the UDI on the device itself 
if the device is intended to be used more than once and intended to be reprocessed before 
each use (21 CFR 801.45). The UDI Rule also includes special labeling requirements for 
stand-alone software regulated as a device (21 CFR 801.50).  
The UDI Rule is intended to create a standardized identification system for medical 
devices that adequately identifies devices through distribution and use. As stated in the 
preamble to the UDI Rule, this system makes it possible to rapidly and definitively 
identify a device and some key attributes that affect its safe and effective use (78 FR 
58786). 
Under the UDI Rule, each labeler must use one or more systems operated by an FDA-
accredited issuing agency to assign UDIs that appear on device labels, on device 
packages, and, as applicable, on devices themselves as direct markings (21 CFR 801.20, 
801.45, and 830.20). In order for there to be an effective identification system, it is 
essential that the FDA-accredited issuing agencies develop and operate systems for the 
assignment of UDIs that allow labelers using these systems to be in compliance with UDI 
labeling requirements.
The UDI must be presented in two forms on the device label and device packages: (1) 
easily readable plain-text; and (2) automatic identification and data capture (AIDC) 
technology (21 CFR 801.40(a)). When a device must bear a UDI as a direct marking, the 
UDI may be provided through either or both easily readable plain-text and AIDC 
technology forms, or through any alternative technology that will provide the UDI of the 
device on demand (21 CFR 801.45(c)).  
III.  Scope
This guidance describes the two forms of a UDI, clarifies the content of the UDI, and 
addresses use of data delimiters that identify specific data elements within the UDI.  The 
guidance also addresses the recommended order of the data in the easily readable plain-
text form of a UDI carrier.  
4 Label and device package are defined at 21 CFR 801.3.
2 Contains Nonbinding Recommendations
This guidance does not apply to universal product codes (UPCs).5 For class I devices, a 
UPC may serve as the UDI to meet the requirements of 21 CFR 801.20 (21 CFR 
801.40(d)). However, a class I device labeler may choose to use a UDI rather than or in 
addition to a UPC (see 21 CFR 801.35). For more information on UPCs, labelers should 
contact an issuer of UPCs.6 Labelers should have proper controls over UPC assignment 
and use to advance the goals of the UDI system.
IV.  Unique Device Identifier (UDI)
Unique device identifier is defined as an identifier that adequately identifies a device 
through its distribution and use by meeting the requirements of [21 CFR 830.20] (21 CFR 
801.3). A UDI is composed of a device identifier (DI) and a production identifier (PI).  
Device identifier is defined as a mandatory, fixed portion of a UDI that identifies the 
specific version or model of a device and the labeler of that device (21 CFR 801.3). 
Production identifier is defined at 21 CFR 801.3 as a conditional, variable portion of a 
UDI that identifies one or more of the following when included on the label of the device:
(i) The lot or batch within which a device was manufactured;
(ii) The serial number of a specific device;
(iii) The expiration date of a specific device;
(iv) The date a specific device was manufactured;
(v) For an HCT/P regulated as a device, the distinct identification code required by 21 
CFR 1271.290(c) of this chapter.
Under 21 CFR 830.20, a UDI must be issued under a system operated by an FDA-accredited 
issuing agency7 and conform to the following international standards incorporated by 
reference in the UDI Rule in 21 CFR 830.10:
 ISO/IEC 15459-2: Information technology - Unique identifiers--Part 2: Registration 
procedures;
 ISO/IEC 15459-4: Information technology - Unique identifiers--Part 4: Individual 
items; and
 ISO/IEC 15459-6: Information technology - Unique identifiers--Part 6: Unique 
identifier for product groupings.
Additionally, the UDI must only use characters and numbers from the invariant character set 
of ISO/IEC 646: Information technology - ISO 7-bit coded character set for information 
interchange.   
5 A UPC means the product identifier used to identify an item sold at retail in the United States. 21 CFR 
801.3.
6 Some FDA-accredited issuing agencies issue UPCs. Contact information for FDA-accredited issuing agencies 
is available at: https://www.fda.gov/medical-devices/unique-device-identification-system-udi-system/contact-
fda-accredited-issuing-agency. 
7 Available at: https://www.fda.gov/medicaldevices/deviceregulationandguidance/uniquedeviceidentification/ 
udiissuingagencies/default.htm. Should FDA ever act as an issuing agency, a labeler would also be permitted to 
use UDIs issued under the system operated by FDA. 21 CFR 830.20, 830.200, and 830.210.
3 Contains Nonbinding Recommendations
It is critical that each FDA-accredited issuing agency develop and operate a system for the 
assignment of UDIs that is consistent with UDI labeling requirements under 21 CFR Part 
801, Subpart B, allowing labelers to confidently use the FDA-accredited issuing agencys 
system to assign UDIs that meet those requirements.
A.  Forms of UDI
The UDI Rule specifies that the UDI on the device label and device packages must be 
presented in both easily readable plain-text and AIDC technology forms (21 CFR 801.40(a)). 
In addition, certain devices are required to be directly marked under 21 CFR 801.45. For 
those devices, the UDI directly marked on the device itself may be provided through either or 
both easily readable plain-text or AIDC technology, or any alternative technology that will 
provide the UDI of the device on demand (21 CFR 801.45(c)).
UDIs, particularly when provided through AIDC technology, are intended to allow rapid and 
accurate data acquisition, recording, and retrieval. The easily readable plain-text form allows 
healthcare professionals, patients, FDA, and other users of the UDI system to read and enter 
the UDI into data systems, such as patient records or reports to FDA, without technological 
assistance. Thus, the easily readable plain-text form may be used as an additional mechanism 
to capture the UDI if the AIDC form cannot be used.  
Figure 1 shows an example of a UDI in both easily readable plain-text and AIDC forms.  
Figure 1. UDI in Easily Readable Plain-Text and AIDC Forms
1.  Easily readable plain-text
For purposes of this guidance, easily readable plain-text means human-legible 
interpretation of the UDI data characters. Issuing agencies or other entities may refer to the 
easily readable plain-text form of the UDI as the human readable interpretation (HRI).8 The 
easily readable plain-text form of the UDI must include the DI and, if applicable, PI. It is also 
important for the easily-readable plain-text form of the UDI to include any data delimiter(s) 
8 See, e.g., UDI N48: Unique Device Identification system (UDI system) Application Guide (March 21, 2019)  
Available at: http://www.imdrf.org/docs/imdrf/final/technical/imdrf-tech-190321-udi-sag.pdf. 
4 Contains Nonbinding Recommendations
for the DI and PI. If the data delimiters are not included, an individual may not be able to use 
the easily readable plain-text form of the UDI to identify the device. The easily readable 
plain-text form of the UDI may be presented as a single line or multiple lines of text, and 
should be displayed below or near the AIDC technology form of the UDI. 
FDA does not prescribe the format for any dates in the PI portion of the UDI and does not 
require the easily readable plain-text form of the UDI to comply with 21 CFR 801.18 when it 
includes dates.9 Labelers should refer to the guidelines of their FDA-accredited issuing 
agency or contact their FDA-accredited issuing agency with any questions regarding the 
format of the dates within the UDI.
2.  AIDC
AIDC is defined at 21 CFR 801.3 as any technology that conveys the UDI or the DI portion 
of a UDI of a device in a form that can be entered into an electronic patient record or other 
computer system via an automated process. Therefore, while the UDI Rule does not require 
the use of a specific form of AIDC or a specific AIDC technology to convey the UDI, the 
AIDC form of the UDI must be in a format that can be read by a bar code scanner or other 
AIDC technology (21 CFR 801.3 and 801.40(a)). The labeler should ensure that the AIDC 
form of the UDI can be reliably read at the points during distribution and use where device 
identification information is important to capture. Labelers should consult the guidelines of 
their FDA-accredited issuing agency to determine which forms of AIDC are supported by the 
issuing agencys UDI system.  
When possible, FDA recommends the AIDC form of the UDI be displayed in one segment; 
however, it may be split into multiple segments. For example, one UDI may be presented in 
two linear bar codes: one bar code for the DI segment and another bar code for the PI 
segment. These two bar codes should be in near proximity to each other on the device label, 
device packages, and, when required, on the device itself.  
The labeler may choose to use more than one type of AIDC technology on a single device 
label, device package, or device (when applicable), to assist users who may be employing 
different methods of UDI capture technology. For example, a labeler may include a linear (1-
D) bar code and data matrix code (2-D) on the device label, both representing the same UDI. 
In this example, only one easily readable plain-text form of the UDI is required to be on the 
device label (21 CFR 801.40(a)), and it should be in near proximity to one of the AIDC 
forms of the UDI.    
If a labeler chooses a bar code form of AIDC, the bar code form of the UDI should be tested 
for print quality. FDA recommends referring to the following standards and technical 
references for more information on determining the print quality:
9 The required format for a printed expiration date, date of manufacture, or other date intended to be brought to 
the attention of the user of the device included on a medical device label is described at 21 CFR 801.18.  
5 Contains Nonbinding Recommendations
 ISO/IEC 15416: Information technology -- Automatic identification and data capture 
techniques -- Bar code print quality test specification -- Linear symbols; 
 ISO/IEC 15415: Information technology -- Automatic identification and data capture 
techniques -- Bar code symbol print quality test specification  Two-dimensional 
symbols; and
 ISO/IEC TR 29158: Information technology -- Automatic identification and data 
capture techniques  Direct Part Mark (DPM) Quality Guideline. 
21 CFR 801.40(c) specifies that if the AIDC technology form (e.g., RFID technology) used 
to convey the UDI is not evident upon visual examination of the device label or device 
package, the device label or device package must disclose the presence of AIDC technology. 
FDA does not require a specific type of symbol to disclose the presence of AIDC technology 
that is not evident upon visual examination. However, FDA recommends that labelers 
consider using symbols that are internationally recognized, where use of such symbols is 
consistent with 21 CFR 801.15(c).
B.  Content of UDI
For purposes of this guidance, we define UDI carrier as the means to convey the UDI and 
potentially non-UDI elements by using easily readable plain-text and/or AIDC forms. UDI 
carriers may include additional, non-UDI information regarding the device. For example, 
some FDA-accredited issuing agencies may provide for including non-UDI elements, such as 
quantity, in the data string within the UDI carrier. However, FDA does not consider such 
additional non-UDI elements as being part of the UDI. As such, data delimiters for additional 
non-UDI elements should be different than the DI and PI data delimiters in the UDI.
Under 21 CFR 801.40(b), the easily readable plain-text and AIDC forms of a UDI must 
include: (1) a device identifier segment; and (2) a production identifier segment that conveys 
one or more of the identifiers enumerated in the definition of a production identifier at 21 
CFR 801.3 when included on the device label. The device identifier segment and the 
production identifier segment cannot include non-UDI elements or data delimiters for non-
UDI elements.  
The UDI Rule does not require any of the five identifiers comprising a PI to be on the label. 
However, other regulations may require one or more of the identifiers comprising a PI to be 
on the label. For example, under 21 CFR 1271.290(c), manufacturers of human cells, tissues, 
and cellular and tissue-based products (HCT/Ps) are required to assign and label HCT/Ps 
with a distinct identification code. In addition, if the labeler includes any of the identifiers of 
which a PI is composed on the label, then for all devices required to bear a UDI other than 
class I devices,10 the identifier must also be included in the PI segment of the UDI (21 CFR 
801.30(d) and 801.40(b)). 
10 FDAs Product Classification database is available at: 
https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpcd/classification.cfm. 
6 Contains Nonbinding Recommendations
There are some situations where a UDI may comprise a DI only. For example, if a class II 
device does not include any of the five identifiers of which a PI is composed on the label, 
then a PI would not be required in the UDI. In addition, the UDI of a class I device is not 
required to include a PI (21 CFR 801.30(d)). However, the labeler of a class I device may 
voluntarily include a PI in the UDI.
C.  Data delimiters
For the purposes of this guidance, data delimiter means a defined data character or set of 
data characters that identifies specific data elements within an encoded data string 
represented in the UDI carrier.11 Data delimiters are used to identify the information that 
immediately follows them, and data delimiters vary based on the UDI system established by 
each FDA-accredited issuing agency.12  
Data delimiters are key to UDI comprehensibility and utility. A data delimiter indicates and 
distinguishes each data element within the data string represented in the UDI carrier, and 
inclusion of data delimiters is important for both the easily readable plain-text and AIDC 
forms of the UDI. Data delimiters allow users to parse the DI and PI in the easily readable 
plain-text form of the UDI, as well as to verify that the information encoded in the AIDC 
form of the UDI matches the easily-readable plain text form of the UDI. The data delimiters 
also enable the UDI to be parsed into electronic systems once scanned. Importantly, data 
delimiters allow the UDI to be distinguished and captured separately from any non-UDI 
elements that may be represented in the UDI carrier. In addition, if non-UDI elements are 
included in the UDI carrier, separate data delimiters for these non-UDI elements should be 
included. Without appropriate data delimiters to identify non-UDI elements, individuals may 
not be able to use the easily readable plain-text form of the UDI to identify a device and 
computer systems may not be able to capture accurately the UDI in AIDC form via an 
automated process.
11 The term data delimiter, as used in this guidance, corresponds to the term qualifier as used in ISO/IEC 
15459-3: Information technology  Automatic identification and data capture techniques  Unique 
identification Part 3: Common rules [third edition], and UDI N48: Unique Device Identification system (UDI 
system) Application Guide (March 21, 2019),-- http://www.imdrf.org/docs/imdrf/final/technical/imdrf-tech-
190321-udi-sag.pdf. 
12 FDA reviewed the UDI format of each issuing agency as part of its process for accrediting issuing agencies 
under 21 CFR 830.100 and 830.110.  The data delimiters used within the UDI formats of FDA-accredited 
issuing agencies can be found in the UDI Formats by FDA-Accredited Issuing Agency document, available at: 
www.fda.gov/downloads/MedicalDevices/DeviceRegulationandGuidance/ 
UniqueDeviceIdentification/UDIIssuingAgencies/UCM489869.pdf, on the UDI webpage (www.fda.gov/udi). 
For more information on encoding data delimiters, labelers should refer to the guidelines of their FDA-
accredited issuing agency or contact their FDA-accredited issuing agency. 
7 Contains Nonbinding Recommendations
D.  Order of the data represented in the easily readable 
plaintext form of UDI carrier
In the easily readable plain-text form of the UDI carrier, the UDI should precede any non-
UDI elements. The easily readable plain-text form of the UDI should be ordered to specify 
the DI first, followed by the PI (if any). If there are any non-UDI elements in the UDI carrier, 
the non-UDI elements should follow the PI that is part of the UDI in the easily readable 
plain-text form. For example, if the label of a particular device bears an expiration date and 
quantity, and the labeler wishes to include the quantity in the UDI carrier, the easily readable 
plain-text of the UDI carrier should display the data delimiter for the DI, followed by the DI; 
the data delimiter for expiration date, followed by the expiration date PI; and lastly, the data 
delimiter for quantity, followed by the quantity. While FDA does not prohibit the inclusion 
of quantity in the UDI carrier, quantity is not considered part of the UDI and the data 
delimiter for quantity should be different than the DI and PI data delimiters in the UDI. For 
more information on including certain non-UDI elements in the UDI carrier, labelers should 
refer to the guidelines of their FDA-accredited issuing agency or contact their FDA-
accredited issuing agency.  
E.  StandAlone Software
There are different labeling requirements for stand-alone software depending on whether or 
not it is distributed in packaged form (21 CFR 801.50). For stand-alone software that is not 
distributed in packaged form, the UDI labeling requirements are met if the UDI is provided 
through either or both of the following and the version number is conveyed in its PI: 
 an easily readable plain-text statement displayed whenever the software is started; or
 an easily readable plain text statement displayed through a menu command (e.g., an 
about command) (21 CFR 801.50(a)).  
For stand-alone software that is distributed in packaged form, 21 CFR 801.50(a) does not 
apply. The stand-alone software must provide its UDI as an easily readable plain-text 
statement displayed whenever the software is started or through a menu command (21 CFR 
801.50(b)). Additionally, the device label and device packages must also bear a UDI in both 
easily readable plain-text and AIDC forms (21 CFR 801.20(a) and 801.40(a)).13  As 
explained above, when the lot or batch within which a device was manufactured is included 
on the device label, the lot or batch must be included in the PI (21 CFR 801.3 and 801.40(b)). 
Software version is included in the definition of lot or batch at 21 CFR 801.3.14  Therefore, 
when a labeler of stand-alone software required to bear a UDI includes a software version on 
the label, it must be conveyed through the PI (21 CFR 801.3, 801.50(b); see also 78 FR 
58794).  
13 See also 78 FR 58804.
14 Lot or batch is defined at 21 CFR 801.3 as one finished device or more that consists of a single type, 
model, class, size, composition, or software version that are manufactured under essentially the same conditions 
and that are intended to have uniform characteristics and quality within specified limits.  
8