The ISO international standard for country codes is ISO-3166, which provides several representations of names for countries (ISO-3166-1) and their subdivisions (ISO-3166-2):
- Country and Subdivision names
- 2-letter codes
- 3-letter codes
- numeric codes
The US government has created a profile of ISO-3166 called GENC (Geopolitical Entities, Names, and Codes) that allows it to conform to the U.S. Board on Geographic Names (BGN) and other US Government recognition policies. The US FDA data standards catalog states that GENC should be used for "Any database, report, or submission that stores and/or displays Countries and their Principle Subdivisions". Other countries may also require the use of specific ISO-3166 profiles. In the majority of cases, the names and codes in ISO-3166 and GENC are fully aligned. However, there are a small number of exceptions that should be noted:
- Slight difference in names, but no difference in 2-letter, 3-letter, and numeric codes, e.g.,
- ISO "French Southern Territories" vs. GENC "French Southern and Antarctic Lands" (for 3-letter code ATF)
- ISO "Congo, Democratic Republic of the" vs GENC "Congo, the Democratic Republic of the" (for 3-letter code COD)
- ISO groups places which GENC separates, e.g.,
- ISO "Svalbard and Jan Mayen" (SJM) maps to separate entities in GENC, "Svalbard" (XSV) and "Jan Mayen" (XJM)
- ISO "United States Minor and Outlying Islands" (UMI) is separated into 9 distinct codes for islands or island groups in GENC
- GENC contains codes for locations not covered by ISO-3166, e.g.,
- "Diego Garcia" (DGA)
- "Bassas da India" (XBI)
For CDISC-compliant data submissions to the US FDA, GENC should be used to populate, at minimum, the DM.COUNTRY variable and two trial summary parameters: FCNTRY/Planned Country of Investigational Sites; MNFCNTRY/Country of Manufacture. However, many companies are still using ISO-3166 for data submissions to the US FDA. Given the majority of overlap between ISO-3166 and GENC, it mostly doesn't matter whether ISO-3166 or GENC is used since the data would be identical. However, if data is coming from subjects located at a site in a politically sensitive location or a small island, GENC should be consulted to ensure the correct codes are used.