Laboratory Question for the Week of March 30, 2026

Question:

What are the X{EPSU} modifiers used in laboratory services?

Answer:

CMS has historically referred collectively to the four new modifiers as the X{EPSU} modifiers, but now typically lists them individually. The descriptors of the modifiers are self-explanatory. Specifically:

•  XE—separate encounter: A service that is distinct because it occurred during a separate encounter
• XP—separate practitioner: A service that is distinct because it was performed by a different practitioner
• XS—separate structure: A service that is distinct because it was performed on a separate organ/structure
• XU—unusual non-overlapping service: The use of a service that is distinct because it does not overlap usual components of the main service.

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