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.
Denial codes that point at this modifier
The corrective actions we publish for these CARCs name modifier XS. Read the denial first: the modifier only helps where the edit and the documentation both support it.
- CO-97The benefit for this service is included in the payment/allowance for another service/procedure that has already been adjudicated.
- CO-236This procedure or procedure/modifier combination is not compatible with another procedure or procedure/modifier combination provided on the same day according to the National Correct Coding Initiative or workers compensation state regulations/fee schedule requirements.
Retrieved 2026-07-18.
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Denial7 provides billing and administrative guidance based on published CMS and X12 sources. It is not medical advice, not a coverage determination, and not a guarantee of payment. NCCI and MUE edits are republished quarterly and payer policies vary by contract. Always confirm against the payer's own current policy before submitting or appealing.