CO Contractual Obligation · CARC Code 97
CO-97

Bundling Denial — Benefit Included in Another Service Already Paid

CO-97 means the payer considers your billed service part of something it already paid. Sometimes it is correct — and you write it off. Sometimes a modifier fixes it in 60 seconds. The key is knowing which situation you are in before you act.

Updated July 2026 · Group code: CO (provider write-off) · Root cause: NCCI bundling edits · Fix rate with correct modifier: ~60–70%
COGroup Code
NCCIPrimary Cause
59 / XE–XUOverride Modifiers
QuarterlyNCCI Table Updates
CO-97 in plain English

CO-97 means the payer already paid for one procedure and considers the denied service to be included in that payment. This is called bundling, and it is governed primarily by NCCI (National Correct Coding Initiative) edits — a CMS-published table of procedure pairs that defines which codes are "component" services of another. The fix depends entirely on whether the NCCI modifier indicator is 0 or 1: 0 means it is a final write-off no matter what; 1 means the right modifier, applied correctly, gets it paid.

⚠️
Do not use Modifier 59 as a blanket CO-97 fix

Modifier 59 without clinical justification is a compliance violation. OIG Work Plans regularly flag "unbundling" via modifier misuse. If the service was not genuinely distinct from the bundled code, the CO-97 is correct — write it off. Modifier 59 or an X-modifier is only appropriate when documentation supports a truly separate service.

Understanding NCCI

What triggers CO-97: NCCI edits explained

NCCI stands for National Correct Coding Initiative. CMS publishes two types of edits that drive most CO-97 denials. Both update quarterly.

Edit type What it does Modifier indicator Example
Procedure-to-Procedure (PTP)
Most CO-97 denials		 Defines code pairs where one code (column 2) is considered a component of another (column 1). Both cannot be billed together without a valid modifier. 0 = never separately payable
1 = modifier may override		 20610 (joint aspiration) bundles into 27447 (total knee) on same DOS
Medically Unlikely Edits (MUE)
Units denials		 Sets maximum units per date of service for a single procedure code. Billing above the MUE limit triggers CO-97 for the excess units. Varies — some MUEs allow modifier override on separate line items CPT 97110 MUE = 4 units/day; billing 6 units → CO-97 on 2 units
Payer-specific bundling
Commercial payers		 Commercial payers may apply their own bundling logic beyond NCCI. CO-97 can appear even when the NCCI table allows the code pair. Payer's own coverage/bundling policy governs. Payer-specific — check provider manual UHC bundles certain lab panels with E/M visits on same day per their own policy

Look up NCCI PTP edits free at CMS.gov → NCCI Edits files (updated quarterly: Jan, Apr, Jul, Oct). Your clearinghouse may also include NCCI lookup in its scrubber interface.

Step-by-Step Fix

What to do when you see CO-97

The workflow splits at step 2: if the NCCI modifier indicator is 0, you stop and write it off. If it is 1, you evaluate the clinical circumstances and apply the right modifier.

  1. Identify both codes in the bundled pair
    From the ERA/835, find: (1) the denied code — this is the column 2 "component" code, and (2) the code it was bundled into — the column 1 "comprehensive" code. Check the denied claim line and the other procedure codes on the same claim for that date of service. The column 1 code is usually the higher-value service.
  2. Look up the pair in the NCCI PTP table
    Search the CMS NCCI PTP edits table for the column 1 / column 2 pair. Find the modifier indicator. Indicator 0 → stop here, write off the denial. Indicator 1 → continue to step 3. If it is an MUE denial, check the MUE table for your CPT code to confirm the unit limit.
  3. Review the clinical documentation for a genuine distinction
    A modifier only works when it is true. Ask: Was this service performed at a separate encounter or session (→ XE)? On a separate anatomical structure (→ XS)? By a separate practitioner (→ XP)? Is it a service that genuinely does not overlap with the bundled procedure (→ XU)? Pull the chart note and confirm the answer before adding any modifier.
  4. Apply the most specific X-modifier (or 59 as last resort)
    Use XE, XS, XP, or XU as appropriate. If none of those precisely describes the distinction, use Modifier 59. Add the modifier to the denied (column 2) procedure code. Attach the relevant documentation — chart note, operative report, or therapy note — confirming the distinct service. Resubmit as a corrected claim.
  5. For commercial non-NCCI bundling: request the payer's policy
    If the NCCI table allows the pair but the commercial payer still issued CO-97, request their bundling policy in writing from provider relations. Compare to your contract. If their bundling conflicts with your contracted terms, you have a basis for a formal appeal. Track these systematically — one denial is an edit; five denials on the same code pair is a policy issue worth escalating.
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Build NCCI lookups into your pre-submission scrubber

CO-97 is almost entirely preventable at the claim-entry stage. A scrubber that checks NCCI PTP edits before submission catches bundling conflicts before they become denials. Practices without NCCI-aware scrubbing spend 3–5x more staff time on CO-97 rework than those with it. If your clearinghouse doesn't include NCCI scrubbing, it is the first upgrade worth buying.

Modifier Reference

Which modifier fixes a CO-97 denial?

Apply the most specific modifier that accurately describes the clinical situation. Each requires documentation to back it up.

XE
Separate encounter

The service occurred in a different session or encounter on the same date. Example: patient returns to the clinic later the same day for a second, distinct evaluation. Documentation must show separate encounter times.

XS
Separate structure

The service was performed on a different anatomical site or organ. Example: arthroscopy of both left and right knee in the same session. Document the distinct anatomical structures in the operative report.

XP
Separate practitioner

A different qualified provider performed the service. Example: one surgeon performs the primary procedure; a second surgeon performs the add-on separately. Each provider's credentials and documentation must support this.

XU
Unusual non-overlapping

The service does not overlap with the usual components of the bundled procedure. Use when the service is distinct in nature but doesn't fit XE, XS, or XP. Requires the most robust documentation of why it does not overlap.

59
Distinct procedural service — last resort

Use only when none of the X-modifiers accurately apply. CMS considers 59 the catch-all of last resort. It carries higher audit risk. Never use 59 as a default override without confirming a genuine distinction in the documentation.

25
Not for CO-97

Modifier 25 separates a significant, identifiable E/M from a procedure on the same day — it does not fix bundling between two procedure codes. If your CO-97 involves an E/M + procedure pair, Modifier 25 goes on the E/M code and is a different scenario from standard NCCI bundling.

Payer-Specific Behavior

How CO-97 behaves by payer type

Payer Type How CO-97 works here Key nuance
Medicare (Original/FFS) CMS NCCI edits are mandatory and definitive. NCCI PTP and MUE tables are published by CMS and applied uniformly by MACs (Medicare Administrative Contractors). Modifier indicator 0 = truly final. No clinical argument overrides a 0-indicator PTP edit. If indicator is 1 and modifier is correct, Medicare must pay — it is the most enforceable bundling rule.
Medicare Advantage MA plans must follow CMS NCCI edits as a baseline per their contracts. However, some plans apply additional proprietary edits. CO-97 on a code pair with modifier indicator 1 should be overrideable with the correct modifier. If an MA plan issues CO-97 on a pair that NCCI allows with a modifier and you submitted the correct modifier, file a standard appeal — MA plans are required to follow CMS bundling rules.
Medicaid (FFS) Most state Medicaid programs have adopted CMS NCCI edits, but some have state-specific modifications. Some states exclude certain procedure pairs from NCCI rules for Medicaid populations. Check your state Medicaid fee schedule and billing manual. State Medicaid CO-97 appeals go through the state's Medicaid administrative appeals process — not the standard commercial grievance process.
Medicaid MCOs Each MCO may apply its own bundling policies on top of NCCI. CO-97 from a Medicaid MCO should first be checked against NCCI; if NCCI allows the pair with a modifier, submit a corrected claim with the modifier per the MCO's resubmission process. MCO bundling policies vary significantly. Request each MCO's bundling policy manual from provider relations if CO-97 is a recurring issue.
UnitedHealthcare (Commercial) UHC uses NCCI as a base and applies additional proprietary bundling edits, particularly for labs, E/M + procedures, and multi-specialty services. UHC's bundling logic is documented in their Administrative Guide. UHC bundles certain lab panels with same-day E/M codes beyond NCCI. Check UHC's provider manual for specialty-specific bundling rules before billing procedure + E/M combos on the same day.
Aetna / Cigna / BCBS (Commercial) All use NCCI as baseline with plan-specific overlays. BCBS plans vary significantly by state — local BCBS plans may have their own bundling policies that differ from national BCBS guidance. Always reference the local plan's provider manual. After a CO-97 from a commercial payer, always ask: does NCCI allow this pair with a modifier? If yes and your modifier was correct, appeal using the NCCI table as your supporting documentation.
Workers' Compensation Workers' comp payers often apply NCCI edits but may follow state workers' comp fee schedule rules that override NCCI in certain situations. Bundling for surgery + follow-up care is especially common in WC claims. WC CO-97 for surgical global period services requires understanding the state's global period rules, which may differ from Medicare's 0-/10-/90-day global definitions.
Prevention

Prevention checklist: stopping CO-97 before it reaches the payer

CO-97 is one of the most preventable denial types. Every dollar spent on pre-submission scrubbing saves 4–6x in rework costs.

  • Enable NCCI PTP editing in your clearinghouse or billing software — this single setting catches the majority of bundling conflicts before submission. If your software does not have NCCI checking, upgrade or add a clearinghouse that does.
  • Update NCCI tables quarterly — CMS revises edits in January, April, July, and October. Outdated NCCI tables in your scrubber will miss new edits and generate CO-97 denials on code pairs that were previously payable.
  • Train coders on the X-modifier framework — ensure every coder knows when XE/XS/XP/XU applies vs. 59, and understands that modifier use requires contemporaneous documentation. Run annual compliance training on unbundling risk.
  • Review operative reports and procedure notes before submission — for complex surgical or multi-procedure claims, have a coder review the operative report before submission to flag code pairs that may trigger NCCI edits and ensure modifiers are pre-applied with documentation.
  • Build a "known bundling pair" reference list for your top specialties — track recurring CO-97 patterns by code pair and payer. Some pairs that trigger CO-97 repeatedly can be pre-emptively handled with standard documentation templates (e.g., a separate-encounter attestation for common E/M + injection combos).
  • Check MUE limits for high-unit therapy and lab claims — before submitting claims with high unit counts (PT/OT services, repeated labs), verify the MUE for each CPT code. Units exceeding the MUE generate CO-97 for the excess; if clinically justified, split to separate lines with modifier.
  • Monitor CO-97 denial rate by specialty and code pair monthly — a sudden spike in CO-97 often signals a quarterly NCCI update that changed the edit status of a code pair your practice commonly bills together. Identify it within the month, not the quarter.
Appeal Template

CO-97 corrected claim / appeal letter

Use this template when you have confirmed the NCCI modifier indicator is 1 and the documentation supports a distinct service. Replace [bracketed fields] with your specifics.

VIA: Corrected Claim Resubmission / Claims Appeal Department

Date: [Date]

Payer: [Payer Name]

Provider NPI: [NPI]

Provider Name: [Practice / Provider Name]

Original Claim Number: [Claim #]

Patient Account: [Account #]

Date of Service: [DOS]

Denied Procedure Code (Column 2): [CPT — denied code]

Column 1 Comprehensive Code: [CPT — code it was bundled into]


RE: Appeal of CO-97 Bundling Denial — NCCI Modifier Override / Distinct Service


Dear Claims Review / Provider Relations Team:


We are appealing the denial of CPT [denied CPT] under denial code CO-97 on the above-referenced claim. The ERA dated [ERA date] indicated this service was bundled into CPT [column 1 CPT].


We have reviewed the applicable NCCI Procedure-to-Procedure edits (effective [NCCI quarter, e.g., Q3 2026 — July 2026]) for the code pair CPT [column 1] / CPT [column 2]. The NCCI modifier indicator for this pair is 1, indicating that a modifier may be applied when clinical circumstances support separate billing.


In this case, the services were distinct because:

[Select and complete the applicable reason:]
— CPT [denied code] was performed at a separate encounter on [time/session] (Modifier XE applicable)
— OR CPT [denied code] was performed on a separate anatomical structure: [structure] (Modifier XS applicable)
— OR CPT [denied code] was performed by a separate practitioner: [provider name, NPI] (Modifier XP applicable)
— OR CPT [denied code] represents a service that does not overlap with the components of CPT [column 1] because [clinical rationale] (Modifier XU applicable)


We are resubmitting this claim with Modifier [XE / XS / XP / XU / 59] appended to CPT [denied code]. Please find attached: (1) the original ERA/EOB, (2) the relevant NCCI PTP edit table entry confirming modifier indicator 1, and (3) the supporting documentation: [chart note / operative report / therapy note] confirming the distinct service.


We request that the corrected claim be processed and payment issued within [payer's appeal window] days.


Contact:
[Billing Contact Name] · [Phone] · [Email]


Sincerely,
[Practice Administrator / Billing Director Name]
[Practice Name]

Attach the NCCI PTP table entry as a printed screenshot — it removes the payer's ability to dispute the modifier indicator. Many payers resolve CO-97 appeals faster when the NCCI documentation is included in the first submission.

Frequently Asked Questions: CO-97

CO-97 means the benefit for this service is included in the payment for another service or procedure that has already been adjudicated. The payer considers the denied code to be a component of another code already paid on the same claim or same date of service. The most common cause is an NCCI (National Correct Coding Initiative) Procedure-to-Procedure (PTP) edit — CMS publishes a quarterly table defining which procedure code pairs cannot be separately billed without a valid modifier.
Modifier 59 can fix a CO-97 denial only when two conditions are both true: (1) the NCCI PTP table shows a modifier indicator of 1 for the code pair, meaning modifiers are permitted, and (2) the service was genuinely distinct — separate encounter, separate structure, separate practitioner, or genuinely non-overlapping. CMS prefers the more specific X-modifiers (XE, XS, XP, XU) over Modifier 59 and has issued guidance that 59 should be used only when no X-modifier applies. Using 59 without clinical justification is a compliance risk flagged in OIG audit work plans.
The NCCI modifier indicator tells you whether a modifier can override a bundling edit for a specific code pair. Indicator 0 means no modifier will override it — the codes can never be separately billed and the denial is final. Indicator 1 means a modifier may be used if clinical circumstances support separate billing. Look up NCCI PTP edits free at CMS.gov (search "NCCI edits" — look for the Medicare NCCI Edits files under the CMS NCCI page). The tables update quarterly in January, April, July, and October. Most clearinghouses also include NCCI lookup as part of their claim scrubber interface.
No. CO-97 uses the CO (Contractual Obligation) group code, which means the denial is a provider write-off under your contract. You cannot bill the patient for the bundled amount. The only narrow exception is a non-covered service where the patient signed an Advance Beneficiary Notice (ABN) for Medicare or an equivalent financial notice for commercial payers — but this is extremely uncommon in standard bundling denials. Balance billing a patient for a CO-97 adjustment is a contract violation.
CO-97 and CO-45 are completely different denial types. CO-45 is about fee schedule limits — it appears on nearly every contracted claim as the write-off of your billed charge above the allowed amount. CO-97 is about coding relationships — it appears when two procedure codes on the same claim are considered bundled per NCCI or payer policy. CO-45 requires a fee schedule comparison to detect underpayments. CO-97 requires an NCCI lookup and modifier evaluation. They require entirely separate workflows.
Commercial payers are not legally required to follow CMS NCCI edits, but most use NCCI as a baseline and add their own proprietary edits. When a commercial payer issues CO-97 on a code pair that NCCI's PTP table shows as modifier indicator 1, submit a corrected claim with the appropriate modifier and include a copy of the NCCI table entry. If the payer still denies after a valid modifier, request their bundling policy in writing and compare to your provider contract — proprietary bundling that goes beyond NCCI may be contractually challengeable.
Related Codes

Denial codes commonly seen alongside CO-97

CO-45
Charge exceeds fee schedule — the standard contractual write-off on every contracted claim
CO-4
Procedure/modifier mismatch — modifier required or modifier used is invalid for the code
CO-59
Processed based on multiple surgery rules — modifier 51 or surgical pricing applies
CO-151
Units exceed the payer's frequency limit — MUE edit triggered on the claim
CO-236
Procedure combination incompatible per coding rules on same day — NCCI PTP conflict
All codes →
Full CARC & RARC denial code reference with fixes

Seeing CO-97 repeatedly on the same code pairs?

Recurring bundling denials usually mean a scrubber gap or a coder training issue — both are fixable. A free RCM audit identifies which code pairs are driving the volume and where the fix lives.

Get a Free RCM Audit → Denial Management Guide