Can I bill the patient for a CO-97?

No. CO means contractual obligation, so the amount is the practice's write-off. The payer did pay for the work, just inside the payment for another service. Billing the patient would charge them twice for the same care.

Can I just add modifier 59 to get a CO-97 paid?

Only when the record supports it. CMS states that a modifier must not be added to a code purely to get past an edit when the clinical circumstances do not justify it. Adding modifier 59 to force payment is a compliance risk, not a billing shortcut. Check the edit's modifier indicator and your documentation first.

What is a modifier indicator on an NCCI edit?

Every NCCI procedure-to-procedure edit carries an indicator. An indicator of 0 means no modifier can be used to bypass that edit. An indicator of 1 means a modifier may be used when the circumstances genuinely justify it. An indicator of 9 means the edit does not apply. If your pair is a 0, there is nothing to appeal.

Is CO-97 the same as CO-234?

No. CO-97 says the service was paid inside another service that was already processed, so the money went somewhere. CO-234 says the procedure is never paid as its own separate line by that payer. They call for different next steps.

RemitBench/Denial codes/CO-97

CO-97 denial code

CO-97 is not the payer refusing to pay for the work. It is the payer saying it already paid for it, inside the payment for another service on the same claim.

What it means: The payer counts this service as part of another service it has already processed, so it will not pay for it twice.
Who owes the money: Practice write-off The letters CO put the amount on the practice. The patient owes nothing for this line, and billing them would charge them twice for one piece of care.
Is appealing worth it: Only after you check one thing. Look up the code pair in the bundling edit table. If the edit's modifier indicator is 0, no modifier can ever unbundle it and there is nothing to appeal. If it is 1, an appeal or a corrected claim can work when your record supports it.

Do not bill the patient. This is the clearest kind of contractual write-off there is. The payer paid for the service. It just paid for it as part of something else. On Medicare there is not even a route to try: an advance notice of noncoverage does not apply to correct coding situations, so the liability cannot be moved to the patient.

Do not add a modifier to force it through. CMS is explicit that a modifier must not be attached to a code just to get past an edit when the clinical facts do not justify it. That is not a billing trick, it is a compliance problem, and it is the kind of thing audits look for.

Why the payer sent it

Four situations produce nearly all CO-97 lines. Which one you are in decides everything that follows.

1. A bundling edit

Medicare runs a set of rules called the National Correct Coding Initiative. Its procedure-to-procedure edits list pairs of codes that should not be billed together for the same patient on the same day. When you bill a listed pair, the first code is payable and the second one is denied unless a suitable modifier is on it. Most commercial payers run the same edits or their own version.

One caution here, because most articles about this code get it wrong. Not every payer reports a bundling edit as 97. Some use reason code 236, which names the correct coding rules directly. If you are chasing an edit and the code you have is 236 rather than 97, the work below is still the right work.

2. The global surgery period

Surgical codes carry a global period, and follow-up care inside that window is already paid for in the surgery. Medicare marks each code 000, 010, or 090. A 000 code covers the day of the procedure. A 010 code covers 10 days after. A 090 code covers the day before, the day of, and 90 days after. Bill a routine post-op visit inside that window and it comes back as included.

3. It is part of a bigger procedure

Some work is simply a step inside another service. The prep, the approach, and the routine follow-up are counted in the payment for the main procedure. Billing the step separately is called unbundling, and this code is how the payer says no.

4. The payer's own inclusive policy

Commercial payers publish their own bundling rules on top of the national ones. These are in the provider manual, not in any public edit file, so the only way to check is to look up that payer's policy or call and ask which policy was applied.

Remark codes you will see with it

Remark code	What it adds
M15	You billed separately for things the payer treats as parts of one service.
M144	The care before and after the procedure is already paid for in the procedure itself.
N19	This procedure is treated as incidental to the main one.
N20	This service is not payable alongside the other service done that day.
M80	Not covered when done in the same session as a service already processed.

Remark code

What it adds

M15

You billed separately for things the payer treats as parts of one service.

M144

The care before and after the procedure is already paid for in the procedure itself.

N19

This procedure is treated as incidental to the main one.

N20

This service is not payable alongside the other service done that day.

M80

Not covered when done in the same session as a service already processed.

Read the letters in front of the 97

CO-97: The usual pairing from a medical payer you are contracted with. The practice absorbs it. Post it as a contractual adjustment.
OA-97: Bookkeeping. The payer is not putting the amount on either side.
PI-97: The payer cut the line on its own, and the patient does not owe it. Medicare cannot use PI at all. Dental plans use it constantly.
PR-97: The patient owes it. Standard on dental plans when the dentist is not in that plan's network. Unusual from a medical payer you are contracted with, and worth a call there.

This is why the letters matter more than the number. The same reason code 97 can be a write-off or a patient balance depending on who sent it and whether you are in their network. Read the group code on every line rather than assuming it from the code number.

What to do next

Find the other line

CO-97 is always about a pair. Look at the rest of the claim and find which line was paid. That paid code is the one the payer says swallowed this one. Without it you are guessing.
If nothing on the claim was paid: the other service may be on a different claim, or from a different date inside a global period. Check the patient's recent history.
Look up the pair and read its modifier indicator

This is the branch point that decides whether the rest of your afternoon is worth spending. The indicator sits on the edit itself. Use the edit file for the quarter your date of service falls in, not the current one. These files are republished every quarter and indicators do change.
Indicator 0: no modifier can bypass this edit, ever. There is no appeal and no resubmission that will work. Write it off and move on. Indicator 1: a modifier may be used, but only when the clinical circumstances genuinely support it. Go to step 3. Indicator 9: the edit does not apply. Something else caused the denial. Call the payer.
Read the record before you pick a modifier

The order matters. Read what was documented, then choose the modifier that describes it. Choosing a modifier first and hunting for support afterwards is how practices get into trouble.
Nothing in the record makes the services distinct: then they were not distinct. Write it off.
Use the modifier that actually fits

Medicare asks you to use the most specific modifier available and to reach for 59 only when none of the others describe the situation.
Send a corrected claim, or appeal with the record attached

A corrected claim is right when the original was missing a modifier the record supports. An appeal is right when the coding was already correct and you need a human to read the operative note or chart.
Either way: send the documentation. An appeal that just repeats the codes gets the same answer back.

The modifiers, in plain words

These are the ones that can lift a bundling edit when the record supports them.

Modifier	Use it when
XE	The two services happened at separate visits on the same day.
XS	They were done on a separate organ or structure.
XP	A different practitioner did the second one.
XU	The service does not overlap the usual parts of the main service.
59	The services were genuinely distinct and none of the four above describes why. Medicare asks you to use it last, not first.
25	An office visit on the same day as a minor procedure was significant and separate from that procedure.
24	An office visit during a post-op window had nothing to do with the surgery.
57	The visit is where the decision to do the major surgery was made.
58	A second procedure in the post-op window was planned, was more extensive, or followed a diagnostic one.
78	The patient went back to the procedure room unplanned, for something related.
79	A procedure in the post-op window was unrelated to the first surgery.

Modifier

Use it when

The two services happened at separate visits on the same day.

They were done on a separate organ or structure.

A different practitioner did the second one.

The service does not overlap the usual parts of the main service.

The services were genuinely distinct and none of the four above describes why. Medicare asks you to use it last, not first.

An office visit on the same day as a minor procedure was significant and separate from that procedure.

An office visit during a post-op window had nothing to do with the surgery.

The visit is where the decision to do the major surgery was made.

A second procedure in the post-op window was planned, was more extensive, or followed a diagnostic one.

The patient went back to the procedure room unplanned, for something related.

A procedure in the post-op window was unrelated to the first surgery.

What CO-97 gets confused with

Code	How it differs from 97
234	The payer never pays that procedure as its own line, full stop. With 97 the money went into a specific other service you can point at.
236	The code or the code and modifier combination clashes with another procedure. That is a coding conflict, not a payment already made.
B15	A qualifying service had to be billed and covered first, and it was not. That is a missing partner, not a swallowed one.
18	An exact duplicate. The same line was submitted twice. Nothing is bundled.
59	Easy to mix up because 59 is also a modifier number. As a reason code it means the payer applied multiple or concurrent procedure rules and reduced the line, rather than folding it into another.

When not to appeal

The edit's modifier indicator is 0. Nothing you send will change it.
The code is one Medicare never pays on its own. Some codes carry a status that means no separate payment under any circumstances, with or without a modifier. Check the fee schedule status before you build a case.
The service was routine follow-up inside a global period. That is what the global payment covered.
The record does not show a separate encounter, a separate site, or a separate reason. If you have to argue hard to find it, it is not there.
You have not found the paid line yet. Appeal after you know what the payer bundled it into.

There is a real cost to appealing these badly. An appeal that leans on a modifier the record does not support is worse than a write-off, because it puts the claim on the wrong side of a coding rule.

Does CO-97 show up in dental?

Reason code 97 is used heavily in dental. The letters in front of it are usually not CO, and that is the part worth your attention.

In dental the group code is normally PR or PI

Dental plans publish their own mapping from the message printed on the EOB to the codes sent on the electronic remittance. Reading one of those mappings is instructive. Across hundreds of bundling rules, the pattern is the same: PR for a dentist outside the network, PI for a dentist inside it. CO barely appears.

So the medical instinct is the wrong instinct here, in both directions.

Treat every 97 as a write-off and you will absorb balances a non-participating patient genuinely owes.
Treat every 97 as billable and you will bill a participating patient for something your contract says you cannot charge.

Read the two letters on the line. Every time.

The national edits do not cover dental

The correct coding edit files are published for practitioner services, outpatient hospital services, and durable medical equipment. There is no dental file. When a dental plan bundles a dental procedure, it is applying its own written policy, not a national edit, so the modifier indicator work above does not apply. The answer is in that plan's processing policy.

What dental plans actually bundle

The rules follow a pattern once you see it: a smaller procedure treated as a step inside a larger one, or repeat work inside a time window after the original. Real examples from published dental plan policy include:

Routine post-operative visits counted inside the fee for the surgery.
An alveoloplasty billed with a surgical extraction, because the extraction already includes minor bone recontouring.
An incision and drainage billed with an extraction, because removing the tooth generally establishes drainage.
Repeat surgery on the same tooth within a set window, often 24 months, counted inside the original fee.
Osseous surgery treated as including several months of post-operative care.
A prophylaxis billed on the same day as scaling for gingival inflammation.

Notice that some of these can be argued. The alveoloplasty case is a good example: the plan asks for a narrative explaining how far the bone recontouring went beyond what the extraction normally includes. That is the dental version of the documentation branch above.

Two more things worth knowing

Dental plans use reason code 97 for something medical does not have at all: the cheaper alternative clause. When a plan pays for a less expensive treatment than the one you delivered, the difference can arrive as 97 with PR in front of it. That is a real patient balance, not a write-off.

And most dental payers do not print a code on the paper or PDF EOB at all. You get a sentence such as "included in the fee for a completed service", while the code only exists on the electronic remittance. If your office posts from PDFs, you may never see a 97 even though the plan sent one.

Dental work billed to a medical carrier on a medical claim form is a different situation. That claim is judged by medical rules, so everything earlier on this page applies to it.

Related codes

Back to all denial codes

RemitBench reads dental EOB PDFs and turns them into posting-ready lines, in your browser, with no upload. It does not read medical remittances today.

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