A dermatology practice sent us a month of remits with one recurring line: CPT 11102, tangential biopsy, denied CO-97 with remark M15 whenever it was billed on the same day as 17110, destruction of benign lesions. The biller had been appending modifier 59 to the biopsy on resubmission and about half were paying. The other half were denied again, and one payer had sent a letter asking for records on twenty of them. When we read the notes, roughly a third of the biopsies were of the same lesion that was then destroyed. Those should never have been billed separately. The other two-thirds were different lesions and should have been paid on the first submission, with a modifier that said so.
That is the whole NCCI problem in one practice: the edits are mechanical, the modifiers are a claim that the edit does not apply to this encounter, and the note has to back the claim. When it does, the modifier is correct and the denial is wrong. When it does not, the modifier is unbundling, which is the polite word for billing twice for one thing, and it is the kind of pattern that brings a records request.
This article explains NCCI edits and modifier 59 from the ground up: how the edit tables work, what the modifier indicator tells you, when 59 or the more specific X modifiers are legitimate, the pairs that trip office practices most, and what to do with a CO-97 denial.
Key takeaways
- NCCI procedure-to-procedure edits pair a column one code that pays with a column two code that is denied unless a permitted modifier is present and justified.
- The modifier indicator is the whole story: 0 means no modifier will ever bypass the edit, 1 means a modifier may if documentation supports it, 9 means the edit is deleted.
- Modifier 59 is the catch-all; XE, XS, XP and XU say specifically why the services were distinct, and CMS has said it prefers them.
- A CO-97 denial on a column two code is correct if the services were one procedure and wrong if they were distinct; only the note decides which.
- Medically unlikely edits (MUEs) are a separate NCCI table that limits units per line or per day, and modifier 59 does not bypass them.
How the edit tables work
The National Correct Coding Initiative is a CMS program, in place since 1996, that publishes tables of code pairs that should not be reported together for the same patient on the same date of service by the same provider. The tables are updated quarterly, on January 1, April 1, July 1 and October 1; the version in effect from January 1, 2026 is 32.0, and April 1 will bring 32.1. Medicare Administrative Contractors apply the edits automatically. Most commercial payers and state Medicaid programs apply them too, sometimes with their own additions, and the practitioner tables are free to download from CMS, so there is no excuse for a scrubber that does not check them.
Each procedure-to-procedure (PTP) edit has a column one code and a column two code. When both appear on a claim, the column one code pays and the column two code is denied, because the work of the column two service is considered included in the column one service. A glossary line: "bundled" means exactly this, the payment for one service already includes the other. The remit usually shows CO-97 (the benefit for this service is included in the payment for another service) with RARC M15 (separately billed services have been bundled as components of the same procedure), or sometimes CO-236 (procedure combination not compatible).
The third piece of every edit is the modifier indicator. An indicator of 0 means the edit can never be bypassed; the two codes are simply never separately payable together, and a modifier on the claim is ignored or flagged. An indicator of 1 means an NCCI-associated modifier may bypass the edit when the clinical circumstances justify it. An indicator of 9 means the edit has been deleted and is listed for history. Before anyone appends a modifier to a denied line, they should look up the pair and read the indicator. If it is 0, the answer is no, whatever the note says.
NCCI edits and modifier 59: when the X modifiers apply
Modifier 59, distinct procedural service, tells the payer that two services normally bundled were in fact separate: a different session, a different site or organ system, a separate incision or excision, a separate lesion, or a separate injury. It is the most used and most misused modifier in professional billing, and CMS has said for years that it should be the modifier of last resort, used only when no more descriptive modifier fits.
On January 1, 2015, CMS introduced four more specific modifiers, collectively the X modifiers, as subsets of 59. XE is a separate encounter: the services occurred at different encounters on the same date. XS is a separate structure: a different organ or anatomic structure. XP is a separate practitioner: a different clinician performed the second service. XU is an unusual non-overlapping service: the service does not overlap the usual components of the main service. Medicare accepts either 59 or an X modifier, but CMS has stated it may selectively require the X modifiers for particular code pairs, and some Medicare contractors and commercial payers already do. We use the X modifiers by default because they force the coder to name the reason, and a reason that cannot be named is a reason that does not exist.
Other NCCI-associated modifiers that can bypass an indicator 1 edit include the anatomic modifiers (RT, LT, E1 to E4, FA and F1 to F9, TA and T1 to T9, LC, LD, RC, LM, RI), the global surgery modifiers 24, 25, 57, 58, 78 and 79, and 91 for repeat laboratory tests. Modifier 25, in particular, is what separates an evaluation and management visit from a procedure on the same day, and it is the subject of its own rules; it is not interchangeable with 59.
| Common office pair (column one / column two) | Why they bundle | When separate billing is legitimate | Modifier |
|---|---|---|---|
| 17110 destruction of benign lesions / 11102 tangential biopsy | Biopsy of the lesion being destroyed is part of the destruction | Biopsy of a different lesion than the ones destroyed, documented by site | XS on 11102 |
| 20610 major joint injection / 20552 trigger point injection | Injections in the same region are considered one procedure | Trigger point injection in a separate muscle group away from the joint | XS on 20552 |
| 96372 therapeutic injection / 99213 office visit | The visit is considered part of the injection service | A significant, separately identifiable E/M beyond the decision to inject | 25 on 99213 (not 59) |
| 11055 paring of callus / 11721 nail debridement | Both are foot care services on the same day | Different anatomic sites, both medically necessary | XS or 59 on 11055 |
| 97597 debridement / 11042 subcutaneous debridement | Two debridement methods on the same wound are one service | Different wounds, documented separately with measurements | XS on 97597 |
| 93000 ECG / 93010 ECG interpretation | The global code already includes interpretation | Never on the same tracing; a second tracing at a separate encounter | XE if a genuinely separate encounter |
| 36415 venipuncture / 36416 capillary blood draw | One blood collection per encounter | Almost never | Indicator 0 for most pairs; do not append |
Medically unlikely edits: the other table
The second NCCI table is the medically unlikely edits (MUEs), which set the maximum units of a code a single patient would ordinarily receive on one date of service. Each MUE has an adjudication indicator. MAI 1 is a claim line edit: units over the limit on one line deny, but the same code on another line with a modifier may pay. MAI 2 is a date of service edit based on policy or anatomy (you cannot remove more than one appendix); units over the limit deny regardless of how the lines are split, and there is no appeal on the edit itself. MAI 3 is a date of service edit based on clinical benchmarks; units over the limit deny across lines, but a documented appeal can succeed.
The practical error we see is a biller splitting a drug or supply code across lines with modifier 59 to get around an MUE. For MAI 2 and 3 edits that does nothing except create a pattern. If the units are legitimate, bill them on one line and appeal with the record. If a payer publishes its MUE values, load them in the scrubber; CMS publishes most practitioner MUEs, and keeps a small number confidential.
What to do with a CO-97 denial
First, look up the pair in the current PTP table and read the indicator. If 0, the denial is correct, write it off as a contractual adjustment, and fix whatever charge entry rule allowed both codes to go out. If 1, read the note. If the note documents a distinct site, lesion, encounter or practitioner, the denial is wrong: send a corrected claim (frequency code 7) with the appropriate X modifier on the column two code, and attach or be ready to send the note. If the note does not document the distinction, the denial is correct, even though it might have been distinct in fact, and the fix is documentation at the next visit, not a modifier now.
Second, look at the pattern. Pull ninety days of CO-97 and M15 lines by code pair and by provider. Pairs with indicator 0 that keep appearing are a charge capture problem, often a superbill or EHR order set that always fires both codes. Pairs with indicator 1 that deny at a high rate for one provider and not another are usually a documentation habit. Fix the source, not the claim.
Third, never add a modifier at the billing desk without reading the note. That is the line between correcting a denial and unbundling, and it is the line auditors look for. Coders who need practice on real pairs can work them in the Revelrex training EHR, and our denial management team sets up CO-97 worklists that show the indicator next to the line so the first question is answered before anyone opens the chart.
Questions we hear
The payer paid the column two code and denied the column one code. Is that right?
It happens when the column two code was billed with a higher charge or on a later line and the payer's system processed it first, or when a commercial payer's edit set is reversed from Medicare's. Either way, you were paid for one of the two, and the amount at stake is the difference in allowables. Appeal for reprocessing only if the difference is material; otherwise post it and note the payer behavior.
Can we use 59 on an E/M code?
No. Modifier 59 is for procedures. The modifier that separates an E/M service from a procedure on the same day is 25, and it has its own test: the visit must be significant and separately identifiable beyond the usual pre- and post-procedure work. Using 59 on a 99213 gets a CO-4 denial and marks the claim as coded by someone unfamiliar with the rules.
Do Medicaid and commercial payers use the same tables?
Medicaid programs use the Medicaid NCCI tables, which CMS publishes separately and which differ in places from the Medicare tables. Commercial payers mostly license the Medicare tables and add their own edits, which they publish in reimbursement policies. Check the payer's policy when a pair denies that is not in the Medicare table; the appeal argument is different when the edit is the payer's own.
What to do this week
- Download the current practitioner PTP and MUE tables from CMS and confirm your scrubber is running the version 32.0 edits, with 32.1 scheduled for April 1.
- Pull ninety days of CO-97, CO-236 and M15 lines grouped by code pair and provider.
- For each pair, record the modifier indicator; write off and fix charge capture for indicator 0 pairs, and review notes for indicator 1 pairs.
- Replace default use of modifier 59 with XE, XS, XP or XU in your coding policy, with the rule that the note must state the reason.
- Remove any charge entry rule or order set that automatically bills both codes of an indicator 0 pair.
