CO-97 Denial Code: What It Means, Why It Happens, and How to Fix It in 2026

What Is the CO-97 Denial Code?

The CO-97 denial code is a Claim Adjustment Reason Code (CARC) that means the billed service is not separately payable because its cost is already included in the payment for another service or procedure on the claim. In plain terms, the payer bundled the denied line into another service it has already paid, and no additional reimbursement is warranted.

• It is a contractual write-off, not a patient balance: The CO group code stands for Contractual Obligation, which means the amount cannot be billed to the patient. Attempting to balance-bill a patient for a CO-97 adjustment violates most payer contracts and creates compliance exposure.
• NCCI edits drive most CO-97 denials: The National Correct Coding Initiative maintains the code pair edits that trigger bundling. When a submitted code pair matches an NCCI edit, the secondary service is denied with CO-97 unless a distinct-service modifier bypasses the edit.
• Remark codes tell you the real reason: CO-97 rarely appears alone. Paired remark codes like M15, N19, and N390 explain why the payer bundled the service, and the appeal or rebill strategy depends entirely on which remark code is attached.

What CO-97 Actually Means

The full text of CARC 97 reads: “The benefit for this service is included in the payment/allowance for another service/procedure that has already been adjudicated.” That single sentence is the whole logic. A service on the claim was paid, and a different service on the same claim, or a recent related claim, is considered part of that payment. The bundled line pays zero, and the difference is written off under contract.

Two components of the code carry meaning worth pulling apart. The CO prefix identifies the group code, and CO stands for Contractual Obligation. This is a category of adjustment the payer is entitled to make under its contract with the provider, and the amount cannot be shifted to the patient. That distinction matters, since PR (Patient Responsibility) codes and CO codes look similar on a remittance but move in opposite directions on the patient account.

The 97 numeric code identifies the specific reason: benefit included in another service’s payment. Providers often come to us after months of watching CO-97 stack up as low-dollar write-offs on the daily EOB, assuming they are unavoidable. In our experience matching providers with billing partners, that assumption is where practices lose the most on this denial. A large portion of CO-97 denials are appealable, rebillable with a modifier, or coding errors that can be prevented at the front end. Treating them as automatic write-offs turns a fixable process problem into a permanent revenue leak.

For a broader map of how CO group codes appear in the revenue cycle, what CO-45 means in medical billing covers the other high-volume CO adjustment providers see: charge-exceeds-fee-schedule reductions.

What Causes a CO-97 Denial?

Every CO-97 denial traces back to one of a handful of scenarios. Understanding which one applies to a given claim is the first step to deciding whether to write it off, rebill with a modifier, or appeal with documentation.

• NCCI edit bundling. The most common cause. Two codes on the same claim match a CMS National Correct Coding Initiative edit pair, and the secondary code is bundled into the primary. NCCI edits update quarterly, so a code pair that paid last quarter may bundle this quarter.
• Global surgical period. An evaluation and management (E/M) visit or minor procedure was billed within the 10-day or 90-day post-operative global period of a prior surgery. The payer considers routine follow-up bundled into the surgical payment.
• Incidental services. The denied service is considered inherent to the primary procedure. Common examples include specimen collection during a biopsy, dressing changes after minor surgery, or preoperative evaluation on the same day.
• Mutually exclusive procedures. Two codes on the claim describe services that would not normally be performed together, so the payer selects one and bundles the other.
• Duplicate reporting. The same service was billed twice, once as its own line and once as a component of another code, resulting in a CO-97 on the duplicate.
• Payer proprietary bundling. Some commercial payers apply bundling rules beyond NCCI, so a code pair that passes Medicare edits still bundles under Aetna, Anthem, or another carrier’s proprietary logic.

CO-97 Remark Codes: What They Tell You

The single most useful step when working a CO-97 denial is reading the paired Remittance Advice Remark Code (RARC). CO-97 by itself only says a service was bundled. The remark code tells you why, which in turn tells you whether to appeal, rebill, or write off.

These are the RARCs that appear most often alongside CO-97 and what each one signals:

The most common issue we see providers run into on CO-97 is ignoring the remark code and treating every bundling denial the same way. An N19 (incidental) denial and an M15 (separately paid) denial call for opposite responses. Working the remark code first is how strong billing operations recover the appealable claims and write off only what actually should be written off.

How to Fix a CO-97 Denial in 5 Steps

Working a CO-97 denial follows a consistent process. These five steps separate practices that recover this revenue from practices that let it drift to write-off:

1. Read the paired remark code first. Pull the RARC (M15, N19, N390, or another) from the remittance. The remark code determines everything that follows. Do not proceed without it.
2. Check the NCCI edit table. For the specific code pair on the claim, look up whether an NCCI Procedure-to-Procedure edit exists and check the modifier indicator. Indicator 0 means the edit cannot be bypassed. Indicator 1 means a modifier may allow separate billing if documentation supports it.
3. Verify the services were truly distinct. If NCCI allows a bypass, confirm the operative note or encounter documentation shows the two services were performed at separate sites, separate encounters, or by separate providers. Do not append a modifier to force payment on services that were not actually distinct.
4. Rebill with the correct distinct-service modifier. Append modifier 59 or one of the X modifiers (XE for separate encounter, XS for separate structure, XP for separate practitioner, XU for unusual non-overlapping service) to the bundled code line. Do not append the modifier to the primary code.
5. Appeal with documentation if the fix fails. When a rebill is denied a second time and the documentation supports separate billing, file a formal appeal with the operative note, the NCCI reference, and a written explanation of why the services were distinct. Track the timely filing window for appeals, which varies by payer.

CO-97 vs Other Denial Codes

Providers frequently confuse CO-97 with other CO-group and PR-group codes because they can look similar on a remittance. The distinction matters, because the response to each is different. Across the billing companies we vet, a recurring pattern in the strong operators is that they train coders and posters to read the group code and the numeric code together, not one or the other in isolation.

• CO-97 vs CO-45. CO-45 is a fee-schedule adjustment. The billed charge exceeded the payer’s contracted allowable, and the difference is a contractual write-off. CO-45 is not a denial in the technical sense, since a partial payment was made. CO-97 is a full denial of a line item because the service was bundled.
• CO-97 vs CO-16. CO-16 means the claim lacks information necessary for adjudication, typically a missing modifier, invalid diagnosis, or documentation request. CO-16 is corrected by adding the missing information and resubmitting. CO-97 is not about missing information; it is about a bundling rule.
• CO-97 vs CO-236. CO-236 is more specific: it flags a procedure or procedure-and-modifier combination that is not compatible with another procedure billed on the same date, based on NCCI or workers’ compensation state guidelines. CO-236 is essentially a modifier-driven cousin of CO-97.
• CO-97 vs PR-1. PR-1 is a patient responsibility code for deductible amounts. It moves to the patient’s balance. CO-97 is a contractual obligation that cannot be billed to the patient. Confusing the two and billing the patient for a CO-97 adjustment is a compliance error that can trigger contract violations with the payer.

How to Prevent CO-97 Denials

Preventing CO-97 is more efficient than working it after the fact. The practices that see the fewest bundling denials build prevention into the workflow at three points: coding, documentation, and pre-submission scrubbing.

• Review NCCI edits quarterly. CMS updates the NCCI edit tables every quarter. A code pair that paid last quarter can start bundling this quarter, and a billing team that does not track the updates finds out through denials rather than through advance notice.
• Train providers on documentation requirements. Modifier 59 and the X modifiers are only defensible when the documentation supports them. Providers who dictate “separate procedure at a separate site” give the billing team something to work with. Providers who dictate “performed the procedure” leave the biller with no way to justify the modifier.
• Use a claim scrubber that includes NCCI logic. Modern practice management and clearinghouse tools flag NCCI edit hits before submission. Working the flag before the claim goes out is far less expensive than working the denial after it comes back.
• Watch the global surgical period. E/M visits and minor procedures billed within the 10-day or 90-day global period of a prior surgery are a top CO-97 cause. Modifier 24 (unrelated E/M) or modifier 79 (unrelated procedure) is the correct fix when the follow-up work is genuinely unrelated to the original surgery.
• Audit incidental service patterns. If specimen collections, dressing changes, or same-day E/M visits are getting denied consistently, the pattern points to a coding workflow issue rather than a payer problem. Auditing 30 days of these denials usually reveals the fix.

Can You Bill the Patient for a CO-97 Denial?

No. CO-97 is a Contractual Obligation adjustment, which means the payer’s contract with the provider explicitly prohibits shifting the amount to the patient. Billing a patient for a CO-97 write-off is a payer contract violation and, depending on the state, may violate balance-billing statutes.

This is one of the sharpest dividing lines between accurate posting and inaccurate posting. When a payment is posted, the biller must read the group code on each adjustment before deciding whether the balance stays with the practice or moves to the patient. CO group codes stay with the practice as write-offs. PR group codes move to the patient. Confusing the two, especially posting a CO-97 as PR, creates two problems at once: the practice bills a patient for an amount the payer never authorized, and the practice loses the audit trail that would have supported an appeal on the underlying denial.

Frequently Asked Questions