CO-97: Check One Number Before You Appeal

CO-97 means the payer decided one of your codes was already paid for inside another. Before you write an appeal, look up the modifier indicator on that code pair. It takes a minute, and it tells you whether an appeal can succeed at all.

If the indicator is 0, no modifier and no documentation will ever unbundle that pair. Appealing it is not just wasted work. Repeated attempts to override a hard bundle are the kind of pattern that draws audit attention.

What the denial is saying

CO-97 tells you that a service you billed is considered included in the payment for another service on the same claim. One code was paid. The other was absorbed into it.

The CO group code matters as much as the number. It marks the amount as a contractual obligation, which means it is written off and cannot be billed to the patient.

Most CO-97 denials come from the National Correct Coding Initiative, which CMS publishes quarterly. NCCI defines pairs of codes that should not normally be billed together, and payer systems apply them automatically before a human sees the claim.

Column 1 and column 2

Every NCCI procedure to procedure edit pairs two codes.

• The column 1 code is the comprehensive service. It gets paid.
• The column 2 code is the component service. It gets denied as included in column 1.

When you look at the remittance, the denied line is the column 2 code. That matters for the fix, because if a modifier is appropriate it goes on the column 2 code, not the one that paid.

The modifier indicator is the whole decision

Every NCCI edit pair carries a single digit that determines whether the bundle can be broken. Almost nobody checks it before appealing, and it answers the question before you start.

This is the step most billing teams skip. Appending a modifier to an indicator 0 pair does not work, and it never will. The modifier is ignored, the claim denies again, and the pattern of repeated override attempts on a hard bundle is exactly what audit selection looks for.

The edit files are published free on the CMS website and updated quarterly. Checking a pair takes under a minute. Doing it before you appeal rather than after saves the appeal entirely on somewhere between a third and half of these denials.

Indicator 0 means the work is inherent

A hard bundle usually reflects one of two things. Either the column 2 service is a technique or approach that is intrinsic to the column 1 procedure, or the two are clinically impossible to separate.

CMS has already decided, categorically, that no clinical circumstance justifies paying both. Your documentation is not the issue. There is no version of the note that changes the answer.

When the indicator is 1

Now the appeal is worth writing, and the question becomes whether the services were genuinely distinct.

Distinct means a different session, a different anatomic site, a different encounter, or a separate procedure that happened to fall on the same date. It does not mean the work took extra time or effort. Extra effort inside a single service is what the column 1 payment already covers.

X modifiers rather than 59

Modifier 59 is the general purpose way of signaling a distinct procedural service, and it is the most audited modifier in existence precisely because it says so little about why.

CMS created four more specific alternatives, and major payers now prefer them: XE for a separate encounter, XS for a separate structure, XP for a separate practitioner, and XU for an unusual non overlapping service.

These carry less audit risk than 59 because they state the reason rather than asserting distinctness in the abstract. If one of them describes your situation accurately, use it.

Not every payer accepts them, and some still want 59. That is worth confirming per payer rather than assuming, because sending the wrong one produces a second denial on a claim that was correct on the merits.

Bundling that is not NCCI

Not every CO-97 comes from a procedure to procedure edit. Three other causes account for most of the rest.

Global period bundling is the one worth checking carefully, because the fix depends entirely on whether the second service was related to the original surgery. That is a clinical question, not a coding one.

A workflow that stops the wasted appeals

1. Identify which code was denied. It is the column 2 code
2. Look up the pair in the current NCCI edit file and read the modifier indicator
3. If the indicator is 0, close the claim. Do not appeal, and do not resubmit with a modifier
4. If the indicator is 1, read the documentation before choosing a modifier. Decide whether the services were genuinely distinct
5. If they were, choose the most specific X modifier that fits, and confirm your payer accepts it
6. If they were not, close the claim. The bundle is correct

Step three is where the time is saved. A meaningful share of CO-97 denials are correct and unappealable, and knowing which ones inside a minute is worth more than any appeal template.

Prevention beats appeals

Every CO-97 you appeal successfully still cost you a rework cycle and several weeks of aging. The same edit checked before submission costs nothing.

Most practice management systems can screen claims against NCCI edits before they go out, and many have the capability switched off or unconfigured because nobody asked. That is worth an hour with your vendor.

The edits change quarterly, so a scrubber configured three years ago and never updated is checking against rules that have moved.

Modifier 25 sits adjacent to this. It signals a separately identifiable E/M alongside a minor procedure, and misusing it is one of the more common routes to a bundling denial. That is covered in modifier 25 in 2026, including the payers now cutting payment on correctly billed claims.

What to do next

1. Pull your CO-97 denials from the last quarter and check the modifier indicator on each pair
2. Count how many were indicator 0. That number is your wasted appeal effort
3. Ask your system vendor whether NCCI screening is enabled and when the edit tables were last updated
4. Check whether your top payers prefer X modifiers or still want 59
5. Review any claim where modifier 59 was appended more than once to the same pair

CO-97 and CO-45 are both contractual adjustments and are frequently confused. CO-45 explained covers the difference and why neither can be billed to the patient.

Sources

• CMS National Correct Coding Initiative. The edit files and the Policy Manual, published quarterly and free.
• HCPCS modifier lookup. The X modifiers and every other HCPCS Level II modifier, with the CMS release date.
• Your payer’s own reimbursement policy, which decides which modifiers it accepts.

Reference information only. Not billing advice. Verify against the payer before you file.