# Identifiers

All research participants, biospecimens and derived data within HTAN are associated with unique HTAN identifiers.

Research participants are identified with the following pattern:

<participant_id> ::= <htan_center_id>_integer

Where the htan_center_id is the HTAN Center Prefix. (e.g. HTA1, HTA2) Please see HTAN Centers for a full list of HTAN Center prefixes.

Derivative data includes anything derived from a research participant, including biospecimens such as samples, tissue blocks, slides, aliquots, analytes, and data files that result from assaying those biospecimens. These identifiers follow the pattern:

<derivative_entity_id>	::= <participant_id>_integer

For example, if research participant 1 within the CHOP project (HTA4) has provided three samples, you would have three HTAN IDs, such as:

HTA4_1_1
HTA4_1_3
HTA4_1_8

# Special Identifiers

If a single data file is generated from one of those samples, that file could have an HTAN ID such as:

HTA4_1_42

If a single data file is derived from more than one participant, the file identifier may contain a wildcard string e.g. ‘0000’, after the HTAN center identifier. For example:

HTA4_0000_1
HTA4_0000_2
HTA4_0000_3

If a data file is derived from an external control participant, the biospecimen and file identifiers will contain the string ‘EXT’ before the external control participant integer. For example:

HTA4_EXT1_1
HTA4_EXT2_2
HTA4_EXT3_3

If you will be creating HTAN identifiers for a HTAN Center or Trans Network Project (TNP), please also see the step-by-step directions below

# ID to ID linkages

Note that the explicit linking of participants to biospecimens to assays is not encoded in the HTAN Identifier. Rather, the linking is encoded in explicit metadata elements (see Relationship Model).

# Creating HTAN Identifiers

The following are step by step instructions for HTAN Centers and Trans Network Projects (TNPs) to create and manage HTAN identifiers. HTAN identifiers should be created for all entities (participants, biospecimens and data-files) within individual research projects.

# Step 1: Determine you HTAN Center ID

Please see HTAN Centers to determine your HTAN Center ID. If the data are part of a Trans Network Project (TNP), use the HTAN Center ID assigned to the TNP.

# Step 2: Assign HTAN Identifiers for all Research Participants.

Create a unique HTAN Identifier for each research participant in the following format:

<participant_id>::= <htan_center_id>_integer

e.g. HTA3_1

Each HTAN Center/TNP controls their own namespaces, and therefore owns all identifiers that begins with their prefix. The integer value following <htan_center_id> is determined by the HTAN Center/TNP.

Participant IDs do not need to be consecutive

HTAN Centers/TNPs may choose to use integer blocks to assign groups. For example, CHOP may have four clinical sites, and may wish to reserve HTA4_1 to HTA4_1000 for all patients from site 1, and HTA4_1001 to HTA4_2000 for all patients from site 2. These blocks are entirely up to the research project and not managed by the DCC. The assigned integers in a set of identifiers need not be consecutive.

Leading zeros (e.g. HTA3_01) should not be used in the ID.

# Step 2b [optional]: If needed, assign HTAN identifiers for external controls

Each external control participant, if present, in your atlas must also have a unique HTAN Identifier. These identifiers are meant only for participants without precancerous or cancerous lesions, and therefore explicitly indicate lack of HTAN-relevant clinical data within the identifier itself. These participant identifiers look like:

<participant_id> ::= <htan_center_id>_EXTinteger

For example, if you are part of the Duke research center, and you have three external control research participants, you will need to create three HTAN Identifiers. For example:

HTA6_EXT1
HTA6_EXT2
HTA6_EXT3

As with regular research participants, the HTAN Center/TNP controls their own namespace, and therefore owns all identifiers that begin with the prefix e.g. HTA6_EXT. The integer value following HTA6_EXT is determined entirely by the HTAN Center/TNP.

# Step 3: Assign HTAN Identifiers for all HTAN Biospecimen and Data Files

Derivative entities include anything derived from a research participant, including biospecimens such as samples, tissue blocks, slides, aliquots, analytes, and data files that result from assaying those biospecimens. Each derivative entity in your atlas must also have a unique HTAN Identifier. These identifiers look like:

<derivative_entity_id> ::= <participant_id>_integer

Analogous to research participant IDs, the unique integer value following <participant_id> is determined entirely by the source HTAN Center/TNP. The ID must not have leading zeros.

Special Case Identifers

If a single data file is derived from multiple participants, the file identifier can contain a wildcard string, e.g. ‘0000’, after the HTAN center identifier. For example:

HTA4_0000_1
HTA4_0000_2
HTA4_0000_3

If a data file is derived from an external control participant, the biospecimen and file identifiers will contain the string ‘EXT’ before the external control participant integer (see Step 2b, above). For example:

HTA6_EXT1_1
HTA4_EXT2_2
HTA4_EXT3_3

# Step 4: Keep Track of all Metadata Associated with Entities

Complex relationships among entities can emerge in any research study. For example, one or more samples may be collected from a research participant at multiple times, and each of those samples processed through a variety of analytic workflows. It is recommended that each HTAN Center/TNP maintain their own mechanism for storing annotation of entities and relationships among those --- for example, many atlases already have in place LIMs systems or spreadsheet-based systems.