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SDTM Variables

Variables are the individual data elements within SDTM domains.

Variable Categories

Identifier Variables

Identify the study, subject, and domain.

VariableLabelDescription
STUDYIDStudy IdentifierUnique study ID
DOMAINDomain AbbreviationTwo-letter domain code
USUBJIDUnique Subject IDUnique across all studies
SUBJIDSubject IDSubject ID within study
SITEIDStudy Site IdentifierSite number

Topic Variables

Describe what was observed.

DomainVariableDescription
AEAETERMAdverse event term
CMCMTRTMedication name
LBLBTESTLab test name
VSVSTESTVital sign test

Timing Variables

Capture when observations occurred.

VariableLabelDescription
–DTCDate/TimeISO 8601 date/time
–STDTCStart Date/TimeStart of observation
–ENDTCEnd Date/TimeEnd of observation
–DYStudy DayStudy day number
VISITNUMVisit NumberNumeric visit identifier
VISITVisit NameVisit label

Qualifier Variables

Provide additional context.

TypeExamplesDescription
Grouping–CAT, –SCATCategory, subcategory
Result–ORRES, –STRESCOriginal/standard result
Record–SEQ, –GRPIDSequence, grouping
Synonym–DECOD, –MODIFYCoded/modified terms

Variable Naming Conventions

Prefix Pattern

Most variables use a domain-specific prefix:

  • AE + TERM = AETERM
  • VS + TESTCD = VSTESTCD
  • LB + ORRES = LBORRES

Common Suffixes

SuffixMeaningExample
--TESTCDTest CodeVSTESTCD, LBTESTCD
--TESTTest NameVSTEST, LBTEST
--ORRESOriginal ResultVSORRES, LBORRES
--ORRESUOriginal UnitsVSORRESU, LBORRESU
--STRESCStandardized Result (Char)VSSTRESC
--STRESNStandardized Result (Num)VSSTRESN
--STRESUStandardized UnitsVSSTRESU
--STATStatusVSSTAT (NOT DONE)
--REASNDReason Not DoneVSREASND
--LOCLocationVSLOC
--DTCDate/TimeVSDTC, AESTDTC

Data Types

Character Variables

  • Text values
  • Max length: 200 characters (XPT V5)
  • Example: AETERM, VSTEST

Numeric Variables

  • Integer or floating-point
  • Example: AGE, VSSTRESN, LBSTRESN

Date/Time Variables

ISO 8601 format:

  • Full: 2024-01-15T09:30:00
  • Date only: 2024-01-15
  • Partial: 2024-01, 2024

Variable Requirements

Required Variables

Must be present and populated for every record.

DomainRequired Variables
AllSTUDYID, DOMAIN, USUBJID
DMRFSTDTC, RFENDTC, SITEID, ARM, ARMCD
AEAETERM, AEDECOD, AESTDTC
VSVSTESTCD, VSTEST, VSORRES, VSDTC

Expected Variables

Should be present when applicable.

DomainExpected Variables
AEAEENDTC, AESEV, AESER, AEREL
VSVSSTRESN, VSSTRESU, VISITNUM

Permissible Variables

Can be included if relevant data exists.

Controlled Terminology

Variables requiring controlled terminology:

VariableCodelist
SEXSex
RACERace
ETHNICEthnicity
COUNTRYCountry
AESEVSeverity
AESERNo Yes Response
VSTESTCDVital Signs Test Code
LBTESTCDLab Test Code

Variable Metadata

Label

40 characters max (XPT V5):

  • Descriptive text
  • Example: “Adverse Event Reported Term”

Length

Define appropriate length for each variable:

  • Consider actual data values
  • XPT V5 max: 200 characters

Order

Maintain consistent variable ordering:

  1. Identifier variables
  2. Topic variables
  3. Qualifier variables
  4. Timing variables

Next Steps