Claim denials don’t just slow down your revenue. They erase it. In 2025, Experian Health’s 3rd Annual State of Claims Survey found that 41% of healthcare providers had at least 1 in 10 claims denied, marking the third consecutive year of increases. Among the most common culprits is the CO 97 denial code, and it’s also one of the most consistently misworked denials in any billing department.
This guide breaks down what CO 97 actually means, why it fires, and exactly how to work through it, from pulling the remittance to filing an appeal.
Key Takeaways
- CO 97 means a billed procedure is bundled into another service already adjudicated. The provider cannot bill the patient for the denied amount.
- As of Q2 2026, CMS maintains over 3.1 million active NCCI code pair edit rules. Every unmodified bundled claim hits one of them (CMS.gov, 2026).
- Modifier 59 or an X modifier (XE, XS, XP, XU) can override CO 97, but only when the NCCI pair carries a modifier indicator of “1” and documentation supports a genuinely distinct service.
- Between 35-60% of denied claims are never resubmitted (AHIMA Journal, 2024), turning a recoverable CO 97 into permanent revenue loss.
What Is the CO 97 Denial Code?
CO 97 is a CARC, a Claim Adjustment Reason Code, with a specific meaning: “The benefit for this service is included in the payment/allowance for another service/procedure that has already been adjudicated.” The “CO” prefix stands for Contractual Obligation. That matters because it means the provider cannot bill the patient for the denied amount. This is not a patient responsibility. It is a provider write-off under the payer contract.
The code is governed by CMS’s National Correct Coding Initiative (NCCI). In Q2 2026, the CMS NCCI database contains over 3.1 million active code pair rules, updated every quarter (CMS.gov, Medicare NCCI PTP Edits, April 1, 2026). Every time a claim hits one of those pairs without the right modifier, CO 97 fires automatically.
The denial doesn’t mean the procedure wasn’t performed. It means the payer considers it a component of something else they already paid for.
As of Q2 2026, CMS NCCI contains over 3.1 million active Procedure-to-Procedure (PTP) edit pairs, updated quarterly. CO 97 fires whenever a billed CPT code falls under one of those pairs and no valid override modifier is present. (CMS.gov, NCCI PTP Edits, April 1, 2026)
Here is your step-by-step guide to searching NCCI PTP tables on CMS.gov
Why Does a CO 97 Denial Happen?
In 2023, the administrative cost to rework a single denied claim rose to $57.23, a 30.6% jump from $43.84 the year before, according to Premier, Inc. (cited in the Aptarro 2025 RCM Benchmark Report). Knowing the exact reason CO 97 fired is the difference between a fast recovery and wasted rework on an unwinnable denial.
Three root causes drive nearly all CO 97 denials:
1. NCCI Bundling Edits (Most Common)
One CPT code is classified as a Column 2 component of a Column 1 code. Payers pay only the Column 1 code and deny the Column 2 with CO 97. A classic example: billing 99213 (office visit) alongside 93000 (EKG routine) on the same claim without appending Modifier 25 to the E/M. The EKG gets denied as bundled.
2. Global Surgical Package Inclusions
Pre-operative visits, routine post-op follow-ups, and some intraoperative services are included in the global surgical package period (10-day or 90-day). Billing them separately without a modifier that identifies them as distinct triggers CO 97 automatically.
3. Mutually Exclusive Code Pairs
Some CPT codes represent procedures that are statistically or clinically unlikely to be performed on the same patient, same day, same anatomical site. CMS flags these as mutually exclusive pairs. Billing both without documented justification results in CO 97.
Unique Insight: CO 97 doesn’t always mean the claim was coded incorrectly. A large share of these denials fire because a modifier was simply left off a legitimately distinct service. That’s a billing workflow issue, not a coder error, and it’s the fastest category of CO 97 to recover revenue from.
Global surgical package guide 10-day and 90-day global period billing rules
How to Work on CO 97 Denial Code: Step-by-Step
In 2024, between 35% and 60% of denied claims were never resubmitted, according to AHIMA Journal research, representing permanent revenue loss for providers. CO 97 is one of the most recoverable denial types when worked systematically.
Step 1: Pull the EOB or ERA
Identify exactly which CPT code received the CO 97 denial and which code was paid. You need both to identify the NCCI pair. Note the date of service and the payer.
Step 2: Look Up the NCCI Edit Pair
Go to CMS.gov → NCCI Edits → PTP tables. Search for the Column 1 (paid) and Column 2 (denied) code combination. Check the modifier indicator:
- Indicator “0”: No modifier can override this edit. The denial is final. Write it off.
- Indicator “1”: Modifier 59 or an X modifier is allowed if the service was genuinely distinct. Proceed to Step 3.
Step 3: Review Clinical Documentation
Pull the operative note, visit note, or procedure record. Does the documentation support that these two services were distinct: separate anatomical site, separate encounter, or separate practitioner? If yes, the denial is appealable. If no, accept it and educate the provider.
Step 4: Apply the Correct Modifier
When documentation supports a distinct service, append the appropriate modifier:
- XS: Different anatomical site or separate organ/body region
- XE: Separate encounter (different session, same day)
- XP: Separate practitioner performed the service
- XU: Service doesn’t overlap the usual component definition
- Mod 59: Distinct procedural service (last resort when no X modifier fits)
Step 5: Resubmit as a Corrected Claim
Submit a corrected claim (frequency code 7 for institutional; payer-specific for professional). Attach the supporting clinical documentation. Log the resubmission in your denial tracking system with a follow-up date.
Step 6: File a Formal Appeal if Still Denied
Include: the original denied EOB, a CMS NCCI modifier indicator printout showing the modifier is allowed, and the clinical note demonstrating distinctness. According to Health Affairs, Medicare Advantage payers overturn denial appeals in favor of the provider 57% of the time. File before the deadline.
Video Resource: CO-97 Bundled Denial: Why Insurance Pays One CPT and Denies the Other (Published Feb 2026)
Here is the corrected claim resubmission guide → step-by-step instructions for corrected claims by payer type
Claim Denial Rates by Payer Type (2024)
| Payer Type | Initial Denial Rate (2024) |
|---|---|
| Medicare | 8.4% |
| Commercial (average) | 13.9% |
| Managed Medicaid | 15.1% |
| Medicare Advantage | 15.7% |
| ACA Marketplace (in-network) | 19.0% |
Source: AHA / KFF / Aptarro, US Healthcare Denial Rates & Reimbursement Statistics, 2026 data
How to Prevent CO 97 Denials Before They Happen
In 2025, 86% of claim denials were identified as potentially avoidable, according to MGMA and HFMA benchmark data (Aptarro 2025 RCM Benchmark Report). CO 97 sits squarely in that preventable category. Catching the bundling conflict before submission costs nothing. Working it after costs $57.23 per claim on average.
At the clearinghouse / PM system level
Enable NCCI edit-checking in your practice management system or clearinghouse before claims transmit. Most major platforms (AdvancedMD, athenahealth, Kareo, eClinicalWorks) include this as a built-in scrubbing rule. Turn it on if it isn’t already.
At the coder level
- Build a reference list of your 10 most frequently denied code pairs and the correct modifiers for each.
- Add a mandatory NCCI lookup step to the coding workflow for any multi-procedure claim.
- Train coders on the difference between global period inclusions and separately reportable services.
At the billing manager level
Set up a weekly denial trend report filtered by CO 97. If the same code pair appears more than 3-5 times in a week, that’s a systemic issue. Fix it upstream, not claim-by-claim.
From the billing floor: Billers who actively select the correct X modifier, rather than defaulting to Modifier 59, see fewer secondary audit flags from payers. Choosing the right X modifier forces a documentation review that Modifier 59 doesn’t, and that review catches under-documented services before they become a bigger problem.
Providers Reporting >10% Denial Rate (2022-2025)
| Year | % of Providers Reporting >10% Denial Rate |
|---|---|
| 2022 | 30% |
| 2023 | 35% |
| 2024 | 38% |
| 2025 | 41% (3rd consecutive annual increase) |
Source: Experian Health, State of Claims Survey 2022-2025, BusinessWire, September 2025
Video Resource: What Are Remark Codes – CO-97 Bundled Denials: Learn and Fix It (Published Dec 2026)
Here is the complete guide below on how to setup denial trend in your PM system.
Denial trend reporting setup in your PM system
Modifier Selection Quick Reference
| Scenario | Use This Modifier |
|---|---|
| Services at a different anatomical site or body region | XS |
| Services at a separate encounter (different session, same day) | XE |
| Services performed by a different practitioner | XP |
| Service does not overlap the typical component definition | XU |
| None of the above X modifiers fit exactly | Mod 59 (last resort) |
Frequently Asked Questions About CO 97 Denial Code
Can a patient be billed for a CO 97 denial?
No. The “CO” prefix stands for Contractual Obligation, meaning the denied amount is a provider write-off under the payer contract, not a patient responsibility. Billing a patient for a CO-prefixed denial is a compliance violation under most payer agreements. The provider absorbs the loss unless the denial is successfully overturned on appeal.
What is the difference between CO 97 and CO 4?
CO 4 fires when a procedure code is inconsistent with the modifier or place of service billed. CO 97 fires when a service is considered bundled into another procedure already paid. CO 4 is typically a coding or documentation fix; CO 97 is a bundling and modifier issue. They require different resolution paths even though both are contractual denials.
How long do I have to appeal a CO 97 denial?
Most commercial payers allow 90-180 days from the EOB date to file an appeal. Medicare has a strict 120-day redetermination window from the initial determination date. Always verify the exact deadline in the payer provider manual. According to Health Affairs, 57% of Medicare Advantage denial appeals are overturned in the provider’s favor, so file before the deadline.
Does Modifier 59 always fix a CO 97 denial?
No. If the NCCI edit pair carries a modifier indicator of “0,” no modifier can override the bundling edit, the denial stands. Only pairs with a modifier indicator of “1” are eligible for a Modifier 59 or X modifier bypass. Always check the indicator in the CMS NCCI PTP tables before spending time on a corrected claim or appeal.
What is the fastest way to reduce CO 97 volume?
Enable NCCI edit-checking in your clearinghouse or PM system before claims transmit. In 2025, 86% of denials were identified as potentially avoidable according to MGMA and HFMA benchmarks. Catching it pre-submission costs nothing. Working it post-denial costs an average of $57.23 per claim (Premier, Inc., 2023).
Here is your complete Clearinghouse NCCI scrubbing setup
Conclusion
CO 97 is one of the more workable denials in medical billing, but only if you don’t leave it sitting. The code tells you the payer considered your billed service bundled into something else they already paid. Your job is to determine whether they’re right, or whether a modifier and documentation can prove the service was genuinely distinct.
Work it in six steps: pull the remittance, check the NCCI modifier indicator, review the clinical note, append the right modifier, resubmit, and appeal if needed. Prevent future occurrences by building NCCI scrubbing into your pre-submission workflow. Don’t let CO 97 become a write-off by default.
Sources
- Experian Health, 3rd Annual State of Claims Survey — businesswire.com
- KFF, Claims Denials and Appeals in ACA Marketplace Plans in 2024 — kff.org
- American Hospital Association, 2025 Cost of Caring Report — aha.org
- Premier, Inc. via Aptarro, US Healthcare Denial Rates & Reimbursement Statistics 2026 — aptarro.com
- AHIMA Journal via Aptarro, US Healthcare Denial Rates & Reimbursement Statistics 2026 — aptarro.com
- CMS.gov, Medicare NCCI Procedure-to-Procedure (PTP) Edits — cms.gov
- MGMA / HFMA benchmarks via Aptarro, US Healthcare Denial Rates 2026 — aptarro.com
Manikandan is a Revenue Cycle Management (RCM) specialist with over 10 years of hands-on experience in US healthcare billing. He has worked extensively with commercial payers, Medicare, and Medicaid across multiple specialties including surgery, orthopedics, and radiology. Manikandan founded Medical Billing 101 to provide free, accurate denial code guides, CPT coding references, and Medicare billing resources for US medical billing professionals.