Modifier XS: Separate structure
When it is appropriate
Use XS when the column two service was performed on a separate organ or anatomic structure from the column one service, for example a procedure on a different limb or a different organ during the same session.
When it is not appropriate
Do not use XS when the two services address the same organ or structure, or when a bilateral-specific modifier such as 50 already describes the situation more precisely.
CMS preference
Use XS over 59 whenever the separation is anatomic in nature.
Retrieved 2026-07-18.
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