The CO-97 denial code frustrates billers because the service was clearly performed — yet the payer refuses to pay for it separately. CO-97 means the payer considers that service already paid as part of another procedure on the same claim.
Sometimes that bundling is correct and the write-off stands. Other times the two services were genuinely distinct, and the right modifier will unbundle them and recover the payment. Knowing the difference is what separates a clean appeal from a wasted one.
What the CO-97 denial code means
The official X12 definition of CO-97 is: “The benefit for this service is included in the payment/allowance for another service/procedure that has already been adjudicated.”
The CO prefix marks it as a Contractual Obligation — a provider write-off you cannot pass to the patient. In practice, CO-97 means: we paid for the primary procedure, and this second code is considered part of that payment.
Why claims get bundled: NCCI edits
Most CO-97 denials trace back to the National Correct Coding Initiative (NCCI), the CMS program that defines which CPT code pairs should not be billed together. NCCI has two relevant edit types:
- Procedure-to-Procedure (PTP) edits. Two codes that should not be reported together for the same patient on the same day. One is the “Column 1” (paid) code and the other is “Column 2” (bundled).
- Modifier indicators. Each PTP edit has an indicator: 0 = never unbundle, 1 = may unbundle with an appropriate modifier when clinically distinct, 9 = edit deleted.
When you bill a Column 2 code without a permitted modifier, the payer applies the edit and posts CO-97.
When CO-97 is correct — and when to appeal
Before appealing, answer one question: were the two services genuinely separate?
- Leave it as a write-off when the bundled code is an integral part of the primary procedure (for example, a surgical approach billed alongside the main surgery).
- Unbundle and resubmit when the services were distinct — different sessions, sites, organ systems, or encounters — and the NCCI indicator is 1.
Fixing CO-97 with the right modifier
The modifier tells the payer the second service was distinct. The most common choices:
- Modifier 59 — distinct procedural service, the classic unbundling modifier.
- X{EPSU} modifiers — XE (separate encounter), XS (separate structure), XP (separate practitioner), XU (unusual, non-overlapping service). Payers increasingly prefer these more specific subsets over 59.
- Modifier 25 — when a significant, separately identifiable E/M service is bundled into a same-day procedure.
Choosing between them is a frequent source of error, so we cover it in depth in Modifier 25 vs Modifier 59. Never append a modifier just to force payment — unsupported modifiers are a top audit trigger.
How to appeal a CO-97 denial step by step
- Check the NCCI edit. Confirm the code pair is actually bundled and read the modifier indicator (0, 1, or 9).
- Review the documentation. The note must show the services were distinct — different site, session, or encounter.
- Apply the correct modifier to the Column 2 code, not the primary code.
- Submit a corrected claim rather than a brand-new claim, so the payer links it to the original.
- Escalate with a written appeal and the operative or progress note if the corrected claim is denied again.
Prevent CO-97 before you submit
Run claims through an NCCI-aware scrubber before submission, keep documentation that clearly separates distinct services, and train coders on the modifier-1 edits specific to your specialty. For the complete map of adjustment codes you’ll encounter, see our medical billing denial codes guide, and compare CO-97 with the fee-schedule write-off CO-45.
Frequently Asked Questions
What does CO-97 mean in medical billing?
CO-97 means the payer has bundled the service into the payment for another procedure that was already adjudicated. It is a contractual write-off unless you can show the services were distinct.
Can I bill the patient for a CO-97 denial?
No. CO-97 carries the CO (Contractual Obligation) group code, so the amount is a provider write-off and cannot be billed to the patient.
Which modifier fixes a CO-97 denial?
When the NCCI edit allows unbundling (indicator 1) and the services were truly distinct, Modifier 59 or a more specific X{EPSU} modifier (XE, XS, XP, XU) tells the payer they were separate. Modifier 25 applies when a distinct E/M is bundled into a procedure.
How do I know if a CO-97 bundle can be unbundled?
Look up the CPT code pair in the NCCI Procedure-to-Procedure edits. A modifier indicator of 1 means unbundling is allowed with the correct modifier and documentation; 0 means it can never be unbundled.
