If you work in medical billing long enough, certain denial codes start appearing again and again. CO-97 is one of them. It doesn’t always look serious at first, but it quietly drains revenue when it shows up repeatedly.
This denial usually means the payer believes a billed service is already included in another procedure. In short, the insurer sees the services as bundled and refuses to pay for the extra line item.
Many practices underestimate how often this happens. Industry data shows that CO-97 denials can affect five to ten percent of claims revenue in some organizations. The frustrating part is that most of these denials are not complicated problems. They are small billing mistakes that could have been caught earlier.
Once you understand the patterns behind CO-97 denials, preventing them becomes much easier. Below are the most common reasons billers encounter this denial and the practical steps that help avoid it.
1. Billing Procedures That Are Already Bundled
The most frequent cause of a CO-97 denial is billing two services that payers consider part of the same procedure.
Under National Correct Coding Initiative rules, certain procedures are automatically grouped together. When those codes appear separately on a claim, the system flags the secondary service as bundled.
For example, some post-operative services are already included in the main surgical CPT code. Submitting those services separately almost guarantees a denial.
A quick review of NCCI edit tables before claim submission can prevent this situation. If the services were separate, the correct modifier may need to be applied.
2. Missing Modifiers That Clarify Separate Services
Modifiers often decide whether a claim gets paid or rejected.
When two procedures happen on the same day, modifiers such as 25, 59, or 51 help explain that the services were independent and medically necessary. Without them, the payer’s system usually assumes the services belong to a bundled procedure.
A typical example occurs when a patient receives a procedure and also has a separate evaluation and management visit during the same appointment. If Modifier 25 is missing, the payer may reject the E/M service entirely.
Interestingly, many practices recover these denials during appeals. When documentation clearly supports the service, approval rates can be surprisingly high.
Still, prevention is easier than appeal work. Consistent modifier training for coding and billing teams helps reduce this type of denial significantly.
3. Duplicate Claims Sent by Accident
Sometimes CO-97 denials happen for a very simple reason: the claim was submitted twice.
A duplicate claim usually starts with a rushed resubmission. The first claim hasn’t finished processing, but another one gets sent anyway. When the payer system sees two identical services dated the same day, it assumes one shouldn’t be paid. A denial follows.
Most billing software now includes claim scrubbers that flag duplicates before submission. The alerts are helpful, but they’re easy to ignore during heavy billing cycles.
Spending a moment reviewing claim history before resubmitting can prevent the mistake and save a lot of time fixing it later.
4. Services Billed During the Surgical Global Period
Surgical procedures often come with a built-in follow-up period. During this time, certain services are already included in the surgical payment.
Depending on the procedure, that global period may last 10 or 90 days. If billers submit additional services within that window, payers usually assume they are part of the surgical package.
However, patients do sometimes return with unrelated issues. When that happens, the claim needs a modifier that shows the visit was separate from the original surgery.
Modifier 24 is commonly used for this situation. Without it, the payer system automatically treats the visit as bundled and denies the claim.
5. Documentation That Doesn’t Explain the Difference
Sometimes services are truly separate, yet a CO-97 denial still shows up. The usual reason is weak documentation. Payers read clinical notes to see why multiple services happened during the same encounter. When the record simply lists procedures without explaining their role, the system may treat them as connected.
That misunderstanding leads to denials.
It can be prevented by stronger documentation. Doctors are expected to state the reason why every service was medically justified and how it varied with the primary procedure. Having that amount of detail in the chart, billers are better placed to use modifiers accordingly and substantiate the claim when it comes to reviews or appeals.
6. Incorrect CPT Code Pairings
Coding combinations are another reason CO-97 denials happen. Some CPT codes cannot appear together because they represent overlapping services. If both codes are submitted on the same claim, payer systems apply bundling edits automatically.
That’s where coding updates matter. NCCI edit tables change throughout the year, and outdated code pairings can quietly remain in billing systems.
7. Payer-Specific Coverage Rules
Even when coding rules are followed correctly, payer policies can still cause denials.
Some insurers treat certain services differently than others. For example, after-hours service codes like 99051 may not be reimbursed in facilities that operate around the clock. In other cases, specimen collection charges may be bundled with laboratory testing.
These differences justify why billing teams should scan through payer guidelines on a regular basis.
A service that is reimbursable under one insurer might be bundled under another.
Preventing CO-97 Denials Before Claims Are Submitted
The easiest way to handle CO-97 denials is to prevent them in the first place. Once a claim gets rejected, fixing it usually takes more time than the original submission. Many billing teams now run claims through NCCI and payer-specific edit checks before sending them out. That simple step catches conflicts early.
Training also matters. Employees with a clear understanding of the rules of modifier use and global periods commit fewer errors when coding.
Conclusion
The CO-97 refusals do not occur frequently due to a single significant error. More frequently, they are due to minor quibbles, such as the presence of missing modifiers, packaged services, or untidy documentation.
Rapid RCM Solutions assists healthcare organizations in mitigating these avoidable denials by paying close attention to the claims they receive, proper coding habits, and proactive revenue cycle services. Practices can defend against bundling risks prior to claims being submitted to the payer to ensure revenues are protected and reimbursement is not held up unnecessarily.
