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.
Worked example
A surgeon performs a procedure on the left knee and, in the same operative session, a separate procedure on the right shoulder. Both codes would normally bundle under an NCCI edit; XS on the second code documents that the structures involved were anatomically distinct.
Frequently asked questions
When is modifier XS 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 is modifier XS 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.
Can modifier XS bypass an NCCI PTP edit?
Yes, when the edit's modifier indicator is 1 and the services were genuinely distinct.
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.