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When variable content remains unmodified but the name of the SDTM variable cannot be used in the analysis dataset, the prefix “U” (for "unmodified") can be used instead of the 2-letter SDTM domain code. For example, if combining records from Adverse Events (AE) and Medical History (MH) into an analysis dataset, it would likely not be analysis-ready to have body system information spread across 2 variables, AEBODSYS on the rows from the AE dataset and MHBODSYS on the rows from the MH dataset. Instead, a single variable that contains the value from AEBODSYS or MHBODSYS is needed. Using the “A” prefix and calling the variable ABODSYS implies that it is an analysis version of a variable, and that the value of ABODSYS may not be the same as AEBODSYS and MHBODSYS on some records. If no changes are made to AEBODSYS and MHBODSYS, using instead a “U” prefix allows for a single column called UBODSYS but makes it clear that no modifications to the content of the SDTM variables were made.