Modifier XU: Unusual non-overlapping service
When it is appropriate
Use XU when the column two service represents work that does not overlap the usual components of the column one procedure, capturing an unusual, non-overlapping situation that the other X modifiers do not describe.
When it is not appropriate
Do not use XU for a service that is, in fact, an inherent part of the primary procedure's usual work; that is exactly the bundling NCCI intends to enforce.
CMS preference
Use XU over 59 as the more specific choice whenever the situation is genuinely about non-overlapping service components rather than encounter, structure, or practitioner differences.
Denial codes that point at this modifier
The corrective actions we publish for these CARCs name modifier XU. 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.