The List of Denial Codes in Medical Billing Your Team Needs to Know
June 2, 2026
Every billing team sees the list of refusal codes in medical billing on a daily basis, but most practices never take the time to examine it. When a denial occurs, someone resolves it, and the identical code is used again the next month.
Claim adjustment reason codes are the standardized codes payers send back on remittance advice to explain why a claim was adjusted or denied. Reading them correctly is step one. Knowing why they keep appearing is what actually protects revenue.
What Are Claim Adjustment Reason Codes and Why They Matter
Claim adjustment reason codes, commonly called CARCs, tell your billing team exactly where a claim broke down. They appear on the Electronic Remittance Advice after a claim is processed and point to the specific issue blocking payment.
Ignoring the pattern behind these codes is where practices lose the most money. Crowe RCA benchmarking data indicates that the average cost of reworking a single rejected claim is $25. When you multiply it by a month’s worth of recurrent denials, the revenue impact quickly becomes substantial.
How Denial Codes Are Structured
Denial codes follow a prefix system that tells you who carries responsibility for the adjustment:
- CO (Contractual Obligation): The provider absorbs the adjustment based on a payer contract
- PR (Patient Responsibility): The balance shifts to the patient
- OA (Other Adjustment): Used when neither CO nor PR applies
- PI (Payer Initiated): The payer adjusts without the provider being liable
Knowing the prefix before the code number helps your team find the correct solution quickly and saves time.
Hard Denials vs Soft Denials
An appeal is not necessary for every denial. Understanding the distinction dictates how your team allocates its time.
In the event of a hard refusal, the payer will not make any payments until a written appeal with accompanying documents is submitted. A soft denial indicates that further information or a correction is required before the claim can be reprocessed. Most soft denials resolve with a corrected resubmission. Hard denials require clinical records, medical necessity documentation, or authorization evidence to overturn.
Top Denial Codes in Medical Billing and What They Mean
Regardless of size or specialty, all practices use the same denial codes. The most frequent ones, what causes them, and the first thing your team should do are all covered in the table below.
| Code | What It Means | Fix Action |
| CO-16 | Claim missing information needed for processing | Identify the missing field, correct and resubmit |
| CO-18 | Duplicate claim already on file | Confirm true duplicate or corrected claim, resubmit with original reference |
| CO-22 | Coordination of benefits issue, another payer may be primary | Verify payer order, bill correct primary payer first |
| CO-27 | Coverage not active on the date of service | Verify eligibility before visit, correct and resubmit |
| CO-50 | Service not considered medically necessary by payer | Submit clinical documentation supporting necessity, appeal with records |
| CO-96 | Non-covered charge, excluded from patient plan | Review plan benefits, write off or bill patient if appropriate |
| CO-97 | Service included in payment for another procedure | Review bundling rules, apply correct modifier if service is separately payable |
| CO-107 | Related qualifying service was denied, causing this denial | Resolve the foundational denial first, then readdress this claim |
| CO-109 | Service not covered by this payer | Verify coverage, redirect to correct payer or inform patient |
| CO-252 | Additional documentation required before claim can be processed | Locate missing records, attach and resubmit promptly |
| CO-273 | Coverage or program guidelines exceeded | Review frequency limits, appeal with clinical justification if appropriate |
Information and Eligibility Denials
CO-16, CO-18, CO-22, and CO-27 are almost always front-end failures. They trace back to incomplete intake, unverified coverage, or coordination of benefits errors that nobody caught before the claim went out.
CO-16 and CO-22 together account for a large share of avoidable denials across practices. According to industry data, the majority of these trace directly to inaccurate or incomplete patient information collected at intake.
Medical Necessity and Coverage Denials
When the invoiced service does not match what the payer deems covered or clinically justified under the patient’s plan, CO-50, CO-96, CO-97, and CO-109 occur.
CO-50 is one of the highest-volume denial codes across specialties and requires the most detailed response to overturn. A clear diagnosis-to-procedure link in the medical record is the strongest defense against it. CO-97 catches unbundled services that the payer considers included in a primary procedure payment, so checking bundling rules before submission prevents most of these.
Documentation and Authorization Denials
Gaps in the pre-authorization and documentation procedure are indicated by CO-107, CO-252, and CO-273. With the appropriate pre-submission review in place, all three can be largely avoided.
CO-252 is particularly common in high-documentation specialties like orthopedics and home health. The payer is not saying the service is uncovered. It indicates that the file is not complete. CO-107 is a downstream rejection, which means that another claim was rejected before this one. When the underlying denial is healed, this one usually goes away as well.
Why the Same Denial Codes Keep Appearing
Recurring denials are not random. They point to a workflow gap the billing process has not closed. The same codes appearing month after month mean the root cause was never fixed, only the individual claim was corrected.
Front End Failures That Drive Most Denials
Most denial codes are created prior to the patient receiving treatment. Unverified insurance, unrequested authorizations, and unconfirmed intake data all directly contribute to refusal patterns later on.
Steps that eliminate front-end denials:
- Verify insurance eligibility at scheduling and again 24 to 48 hours before the visit
- Confirm coordination of benefits for every patient carrying more than one active plan
- Request and document prior authorization before the service date
- Collect accurate patient demographics at intake and confirm them at check-in
- Flag coverage gaps immediately and resolve them before the appointment proceeds
Coding and Documentation Gaps
CO-4, CO-11, CO-50, and CO-97 almost usually have coding or documentation problems. These codes are frequently caused by a bundled service that is billed separately, a modifier that was left off, or a diagnostic that does not support the treatment.
There are more options than correcting each individual allegation.
It entails checking to see if the same mistake pattern appears in several claims and fixing it at its root. The same codes no longer appear in your monthly reports thanks to Rhode Island Medical Billing’s medical billing services, which include rejection pattern analysis as part of continuous revenue cycle management.
How to Fix and Prevent Denial Codes Before They Hit Revenue
Fixing a denial after it lands is reactive. Preventing it before submission is what moves the revenue needle.
Building a Denial Tracking System
Monitoring denials by provider, payer, and code provides your team with the insight they need to halt recurrent trends. Without this information, the same mistakes keep happening.
A functional denial tracking system covers:
- Monthly denial log sorted by code volume and payer
- Root cause assigned to each denial category
- Resolution timeline tracked per claim
- Staff accountability assigned by denial type
- Monthly trend review to catch new patterns before they compound
Practices that build this structure consistently report measurable reductions in denial rates within the first 90 days.
Denial Codes Stop Being a Problem When the Process Is Right
Denial codes are not the issue. They are symptoms. The real problem sits upstream in intake, authorization, coding, or documentation, and it keeps producing the same codes until the process changes.
Practices that fix denials at the root level stop losing revenue to problems that were preventable from the start. Rhode Island Medical Billing works with practices to identify denial patterns, close the upstream gaps, and build a billing process that submits cleaner claims from day one. If the same codes keep showing up in your remittance reports, reach out to our team for optimal support.
FAQ
What does CO 252 denial code mean?
CO-252 means the payer requires additional documentation or an attachment before the claim can be processed. It is not a coverage denial. Locate the missing records, attach them, and resubmit the claim promptly.
What does CO 107 denial code mean?
CO-107 means a related or qualifying service was denied or unpaid, which caused this claim to be denied as well. Resolve the foundational denial first, then resubmit the dependent claim.
What is denial code CO 273?
CO-273 means the service exceeded the coverage or program guidelines set by the payer, such as a frequency limit or benefit cap. Appeal with clinical justification if the service was medically appropriate.
What is the CO 22 denial code?
CO-22 is a coordination of benefits denial. It means the payer believes another insurer should be billed as primary. Verify the correct payer order, bill the primary insurer first, and resubmit.
