Modifier XU: Unusual Non-Overlapping Service and When to Use It
Modifier XU tells Medicare that a service is distinct because it does not overlap the usual components of the main service. It is the X modifier for content, used when the site, encounter and person are the same but the work is not.
Written by Salman Saeed, CEO and Co-Founder · Reviewed by a Certified Medical Coder · Last reviewed October 2026In short: XU fits diagnostic work that comes before or after treatment, or services the main procedure does not include. It does not fit codes that merely have different descriptors.
What Does Modifier XU Mean?
Modifier XU is a HCPCS Level II modifier defined as "Unusual non-overlapping service, the use of a service that is distinct because it does not overlap usual components of the main service." It has been in the CMS HCPCS file since January 1, 2015, and the NCCI manual says it may be used in place of modifier 59 whenever possible.
XU is the X modifier for content. It does not depend on site, encounter or person. It says the second service did not duplicate any part of what the first service normally includes, which is the question an NCCI edit asks.
When Does XU Fit?
MLN1783722 and the NCCI manual name XU, with 59, in two diagnostic situations at the same encounter. Both rest on the idea that the diagnostic service is separate in time and purpose from the treatment.
| Situation | All of these must be true |
|---|---|
| Diagnostic procedure before a therapeutic one | It is the basis for deciding to do the therapeutic procedure. It occurs before the therapy and is not mingled with services the therapy requires. It clearly gives the information needed to decide whether to proceed. It is not a service that would have been required during the therapy anyway. |
| Diagnostic procedure after a completed therapeutic one | It occurs after the therapy is complete and is not mingled with services the therapy requires. It is not a common, expected or necessary follow-up to the therapy, and it is not an otherwise required part of the therapy. |
If the diagnostic procedure is an inherent component of the surgical or therapeutic procedure, MLN1783722 says not to report it separately at all.
Where Does the NCCI Manual Name XU?
| Setting | XU (with 59) is named when | Where |
|---|---|---|
| Percutaneous intravascular intervention | A diagnostic angiogram is done on the same date by the same provider, or repeated because it is medically necessary to define the anatomy further. A repeat of only part of the study also carries modifier 52. | Chapter IX |
| Anesthesia, ventilation management | The anesthesia practitioner transfers care to another physician and is called back to start ventilation because the patient's status changed. | Chapter II |
| Anesthesia, postoperative pain | An epidural is used for postoperative pain rather than operative anesthesia, or the surgeon asks the anesthesia practitioner to manage pain after the anesthesia care period ends. | Chapter II |
| Sleep testing | Continuous EEG monitoring is a significant, separately identifiable service distinct from the EEG included in the sleep test. | Chapter XI |
| Critical care | A transesophageal probe is placed on the same date as critical care, for TEE monitoring (93318). | Chapter XI |
| Mohs surgery | A diagnostic biopsy and frozen section are done before Mohs surgery (59, XS or XU, or 58). | Chapter III |
What Does an XU Claim Look Like?
An anesthesia practitioner provides anesthesia for a surgery and transfers the patient to the care of another physician in recovery. Later the patient's condition changes, and the anesthesia practitioner is called back to start ventilation.
The manual says that if the practitioner had started ventilation in the recovery area before the transfer of care, the ventilation management would be part of the anesthesia package and would not be reported.
When Is XU the Wrong Choice?
- When the two codes simply have different descriptors. MLN1783722 says not to use 59 or XU to bypass an edit because the codes describe "different procedures", and shows 34833 and 34820 on the same side as the example.
- When the services overlap in the same session, such as a diagnostic study that is part of the therapeutic procedure.
- When a different site, encounter or person is the real reason. Then XS, XE or XP describes it better.
How Does It Sit on the Claim?
On the CMS-1500, enter XU next to the procedure code in box 24D, and note that the form takes up to four modifiers per line per chapter 26 of the claims manual. CMS allows XU on the Column One or Column Two code, per MLN1783722.
The note has to show why the second service did not overlap the first: its purpose, its timing, and the result that drove the decision.
How Does Modifier XU Read on the Form and on the Remittance?
XU sits beside the code in item 24D. It is for a service that did not overlap the main one, so the note, not the form, carries the proof.
Read the group code and CARC on the line. A CO with CARC 236 means the pair was still treated as incompatible. A CO with CARC 97 means the second service was bundled. A CO-4 means XU was refused for that code.
A second service with its own purpose and timing is billed with XU and returns CO-236 for $54.00.
Which Denials Follow a Misused XU?
| Code | X12 description | Usual cause here |
|---|---|---|
| CO-236 | The procedure or procedure and modifier combination is not compatible with another provided the same day under NCCI or workers compensation rules. | XU missing, or edit has an indicator of 0. |
| CO-97 | The benefit is included in the payment for another service already adjudicated. | Payer sees the service as part of the main one. |
| CO-4 | The procedure code is inconsistent with the modifier used. | XU on a code the payer does not accept it for. |
Compare modifier 59. Our billing and coding audits check modifier use. If these denials keep coming back, our denial management team can work them.
Related Codes
- Medicare NCCI Policy Manual 2026, all chapters (revision date 1/1/2026) · CMS
- MLN1783722: Proper Use of Modifiers 59, XE, XP, XS & XU (April 2026) · CMS Medicare Learning Network
- Medicare Claims Processing Manual, chapter 26, item 24D · CMS
- HCPCS Level II quarterly update, October 2026 alpha-numeric file · CMS
- Claim Adjustment Reason Codes · X12
- Medicare Claims Processing Manual, chapter 22, sections 60.1 to 60.3 (group codes, CARC, RARC on the remittance) · CMS
We check every rule, code and deadline against the official source. See our editorial policy.
Common Questions
Straight answers from the team that does the work.
Ask a billing lead directly. A 20-minute call, Monday to Friday, 9am to 5pm Eastern.
01What is modifier XU?
XU is a HCPCS modifier meaning unusual non-overlapping service: a service that is distinct because it does not overlap the usual components of the main service. The NCCI manual says it was added on January 1, 2015, and can be used in place of modifier 59 whenever possible.
02How is XU different from XS?
XS is about place: a separate organ or structure. XU is about content: the second service does not overlap what the main service normally includes. A diagnostic angiogram before an intervention is an XU case. Two lesions in different regions are an XS case.
03Can XU be used just because the two codes have different descriptors?
No. MLN1783722 says not to use modifier 59 or XU to bypass an edit based on the two codes being different procedures. Codes at the same site and the same encounter are not separate and distinct just because their descriptors differ.
04Can a diagnostic test be billed with XU after a procedure?
Only if it comes after the completed procedure, is not mingled with the procedure's own services, and is not a common, expected or necessary follow-up. If it is an included or not separately payable post-procedure service, MLN1783722 says not to report it separately.
05Can XU go on either code of an edit pair?
Yes. MLN1783722 says CMS allows modifiers 59, XE, XP, XS and XU on Column One or Column Two codes, citing Change Request 11168. Confirm that the pair has a modifier indicator of 1, since an indicator of 0 allows no modifier.
Diagnostic and Treatment Codes Bundling?
We check what each service covers against the NCCI pair before billing.