Medical billing denial codes help healthcare providers understand why an insurance claim was denied, reduced, adjusted, or assigned to another party for payment. For medical practices, these codes are more than messages on an Explanation of Benefits or Electronic Remittance Advice. They can reveal problems with eligibility verification, coding accuracy, prior authorization, documentation, payer rules, claim submission, and other parts of the healthcare revenue cycle. A high volume of denied claims can delay reimbursement, increase administrative work, and leave valuable revenue sitting in accounts receivable. That is why an effective denial strategy should focus not only on correcting denied claims but also on preventing the same problems from occurring again.
Some of the codes frequently encountered in medical billing workflows include CO-45, CO-97, CO-16, CO-50, CO-96, CO-18, CO-29, CO-109, CO-151, and CO-197. They cover issues ranging from contractual adjustments and bundling to medical necessity, missing information, duplicate claims, timely filing, incorrect payer information, and missing authorization. Healthcare organizations that combine accurate Medical Billing Services, Medical Coding Services, eligibility checks, claim scrubbing, authorization management, and structured Denial Management Services can identify many of these problems before claims reach the payer.
What Medical Billing Denial Codes Actually Tell You
When a payer processes a medical claim, the Electronic Remittance Advice or Standard Paper Remittance may contain standardized codes explaining why the amount paid differs from the amount billed.
CMS explains that claim adjustments may include three important types of codes:
Claim Adjustment Group Code: Identifies which party generally has financial responsibility for an adjustment.
Claim Adjustment Reason Code (CARC): Explains the overall reason why the claim or service was adjusted.
Remittance Advice Remark Code (RARC): Provides additional information that can clarify the CARC and help the billing team determine what needs to be corrected.
Common group codes include:
CO – Contractual Obligation: Generally represents an amount for which the provider is responsible under payer contracts or applicable requirements.
PR – Patient Responsibility: Indicates an amount assigned to the patient, such as an eligible deductible or coinsurance amount.
OA – Other Adjustment: Used when another adjustment category is appropriate.
Understanding these differences is important because every code should not automatically be handled as an appeal. Some claims need correction and resubmission. Others require documentation, an appeal, contractual adjustment, payer follow-up, or transfer to patient responsibility.
A structured Revenue Cycle Management Services workflow should therefore connect each denial reason with the correct next action rather than allowing every denial to enter the same work queue.
The 20 Medical Billing Denial Codes Facilities See Most
The following medical billing denial codes and adjustment codes commonly appear in healthcare reimbursement workflows. Exact handling can vary according to the payer, provider contract, accompanying RARC, clinical documentation, and applicable coverage policy.
1. CO-45: Charge Exceeds Fee Schedule or Maximum Allowable
CO-45 indicates that the billed charge exceeds the applicable fee schedule, maximum allowable amount, or contracted or legislated fee arrangement.
This is frequently misunderstood as a complete claim denial. In many situations, it represents the contractual difference between the provider’s billed charge and the payer’s allowed amount. X12 specifies that CARC 45 can be used with CO or PR depending on liability.
How to prevent or manage CO-45:
Maintain current payer contracts and fee schedules in the billing system. Compare payer allowed amounts with contracted rates during Payment Posting Services. When the adjustment matches the contract, post it correctly. When reimbursement is below the contracted amount, investigate a potential underpayment before writing off the balance.
2. CO-97: Benefit Included in Another Service
CO-97 means payment for one service is considered included in the payment or allowance for another service that has already been adjudicated.
This frequently relates to procedure bundling.
How to prevent CO-97:
Review coding edits before claim submission. Make sure CPT and HCPCS codes are supported by documentation and verify whether a modifier is appropriate under applicable coding rules. Do not automatically add modifiers simply to bypass a payer edit.
Professional Medical Coding Services can help identify bundling issues before claims leave the practice.
3. CO-16: Claim Lacks Information or Contains Billing Errors
CO-16 indicates that required information is missing or that the claim contains a submission or billing error. X12 requires an accompanying remark code to provide additional information about the problem.
Common problems may include incomplete provider information, incorrect patient data, missing claim fields, or other submission errors.
How to prevent CO-16:
Use claim scrubbing before submission. Verify patient demographics, provider identifiers, claim fields, diagnosis codes, procedure codes, modifiers, and insurance information. When CO-16 occurs, review the accompanying RARC before making corrections.
4. CO-50: Medical Necessity
CARC 50 is used when the payer considers the services non-covered because they are not deemed medically necessary.
The diagnosis, procedure, clinical documentation, or payer coverage policy may not support payment.
How to prevent CO-50:
Check payer medical policies and applicable coverage requirements before performing services that commonly require medical necessity verification. Ensure ICD-10 diagnoses accurately represent the patient’s documented condition and support the billed procedure.
Strong clinical documentation and accurate medical billing and coding are critical.
5. CO-96: Non-Covered Charges
CO-96 relates to non-covered charges. X12 notes that it should be accompanied by an appropriate remark code that provides additional context.
A service can be medically appropriate but still fall outside the patient’s benefit plan.
How to prevent CO-96:
Verify benefits before the service whenever possible. Inform appropriate staff about exclusions, limitations, payer requirements, and patient responsibility according to applicable rules.
Reliable Eligibility Verification Services can reduce avoidable coverage-related denials.
6. CO/OA-18: Duplicate Claim or Service
CARC 18 identifies an exact duplicate claim or service. Current X12 guidance specifies that CARC 18 is generally used with OA, except where certain workers’ compensation regulations require CO.
Duplicate claims can occur when staff resubmit a claim before checking whether the original is still processing.
How to prevent duplicate claim denials:
Check claim status before resubmission. Maintain clear workflows for corrected claims and prevent multiple staff members from independently working the same account.
7. CO-29: Timely Filing Limit Expired
CARC 29 means the time limit for filing the claim has expired.
Every payer may establish different filing requirements, making timely filing management an important part of Claims Management Services.
How to prevent CO-29:
Maintain payer-specific filing deadlines, submit clean claims quickly, monitor rejected claims daily, and track claims that have not been accepted by the payer.
Keep electronic submission and acceptance reports whenever available because they may be important when demonstrating that a claim was originally submitted on time.
8. CO-109: Claim Should Be Sent to Another Payer
CARC 109 indicates that the claim or service is not covered by the payer or contractor receiving it and should be sent to the correct payer.
This may result from incorrect insurance information or coordination of benefits problems.
How to prevent CO-109:
Verify the patient’s active insurance, payer ID, primary and secondary coverage, and coordination of benefits before claim submission.
9. CO-151: Frequency of Services Not Supported
CARC 151 is used when the payer determines that the submitted information does not support the number or frequency of services billed.
For example, a payer may allow a particular test, treatment, or service only at defined intervals unless additional documentation supports more frequent care.
How to prevent CO-151:
Review payer frequency limits before billing repeated services. Ensure clinical documentation clearly supports why the frequency of treatment was medically appropriate.
10. CO-197: Prior Authorization or Precertification Absent
CARC 197 indicates that required precertification, authorization, notification, or pretreatment approval was absent.
This is one of the denial types that should ideally be addressed before the patient receives the service.
How to prevent CO-197:
Create a payer-specific authorization workflow. Determine whether authorization is required during scheduling, obtain it before treatment, verify authorized dates and services, and make sure the authorization information reaches the billing team.
Well-managed Prior Authorization Services can significantly strengthen front-end denial prevention.
11. CO-4: Procedure Code Is Inconsistent With the Modifier
CARC 4 indicates that the procedure code is inconsistent with the modifier used.
Modifier errors can change how a payer interprets a procedure and may affect reimbursement.
How to prevent CO-4:
Review CPT and HCPCS modifier rules, payer-specific edits, and provider documentation. Coding teams should use modifiers only when documentation and coding guidelines support them.
12. CO-11: Diagnosis Is Inconsistent With the Procedure
CARC 11 indicates that the diagnosis is inconsistent with the procedure billed.
The diagnosis submitted may not support the medical reason for the service.
How to prevent CO-11:
Improve documentation and diagnosis-to-procedure validation. ICD-10 coding should represent the documented condition accurately, while procedure codes should reflect the services actually performed.
Regular medical billing audits can identify recurring diagnosis and procedure mismatches.
13. CO-22: Coordination of Benefits
CARC 22 indicates that the care may be covered by another payer according to coordination of benefits.
For patients with multiple insurance policies, the wrong payer may have been billed first.
How to prevent CO-22:
Determine the primary and secondary payer before claim submission. Ask patients about insurance changes and verify coordination of benefits periodically instead of relying entirely on old registration records.
14. CO-27: Expenses After Coverage Terminated
CARC 27 indicates that expenses were incurred after coverage terminated.
Coverage may have been active during a previous visit but inactive on the current date of service.
How to prevent CO-27:
Never assume eligibility remains unchanged. Run insurance verification as close to the date of service as practical and confirm coverage for scheduled procedures.
15. CO-31: Patient Cannot Be Identified as the Payer’s Insured
CARC 31 means the payer cannot identify the patient as its insured member.
Incorrect member IDs, patient names, dates of birth, or outdated insurance information can contribute to this problem.
How to prevent CO-31:
Confirm demographic and insurance information at registration. Compare information entered into the practice management system with the insurance record and eligibility response.
16. CO-119: Benefit Maximum Reached
CARC 119 indicates that the benefit maximum for a particular time period or occurrence has been reached.
Some health plans impose limits on specific services, visits, treatments, or benefit categories.
How to prevent CO-119:
Verify remaining benefits when scheduling services that commonly have utilization limits. Keep staff informed about payer-specific benefit restrictions.
17. CO-125: Submission or Billing Error — Legacy Code
Older denial-code resources may list CARC 125 for submission or billing errors. However, this code is important to treat carefully because X12 shows that CARC 125 was discontinued effective November 1, 2013.
For current claims, billing teams should rely on active CARCs, accompanying RARCs, and current payer guidance instead of building workflows around this discontinued code.
This distinction is particularly important when using older denial-code cheat sheets or training materials.
18. PR-1: Deductible Amount
CARC 1 represents a deductible amount. When paired with PR, it reflects patient financial responsibility rather than a traditional payer denial.
How to manage PR-1:
Verify benefits before the visit when possible, estimate patient responsibility according to available benefit information, post insurance payments accurately, and transfer the appropriate deductible amount to the patient balance.
19. PR-2: Coinsurance Amount
CARC 2 represents coinsurance. Like PR-1, this is generally a patient responsibility rather than a true denial.
How to manage PR-2:
Use accurate eligibility information, payment posting, and patient balance workflows. Do not incorrectly classify routine coinsurance as unresolved insurance accounts receivable.
20. OA-23: Impact of Prior Payer Adjustment
CARC 23 represents the impact of a prior payer’s adjudication, including previous payments or adjustments, and X12 specifies that it is used with group code OA.
This is especially relevant when secondary or tertiary insurance is involved.
How to prevent processing problems with OA-23:
Make sure primary payer information, remittance details, payment amounts, and adjustments are correctly transferred when submitting claims to subsequent payers.
Accurate Payment Posting Services and secondary claim processing can reduce unnecessary follow-up.
Why These Medical Billing Denial Codes Keep Recurring
Most recurring claim denials are not random. They usually point to weaknesses somewhere in the revenue cycle.
One of the biggest sources is the front end of the process. Incorrect patient demographics, outdated insurance information, eligibility problems, coordination of benefits issues, and missing authorization can create problems before the provider has even submitted a claim.
Coding and documentation are another major area. Incorrect ICD-10 codes, CPT errors, inappropriate modifiers, incomplete documentation, bundling problems, and diagnosis-to-procedure inconsistencies can lead to payment delays even when the patient’s insurance information is correct.
Finally, practices may continue seeing the same denial because they correct individual claims without correcting the process that produced them.
For example, repeatedly correcting CO-16 claims is less effective than identifying why required information keeps disappearing from claims in the first place. Likewise, constantly appealing CO-197 claims will not solve a scheduling workflow that fails to identify authorization requirements.
Current search results consistently identify eligibility problems, authorization failures, coding issues, missing information, timely filing, duplicate billing, medical necessity, and coordination of benefits among major causes of medical claim denials.
An effective healthcare revenue cycle management strategy should therefore use denial data as operational feedback.
Practices can strengthen prevention by:
- Verifying insurance eligibility and benefits before services.
- Confirming prior authorization requirements during scheduling.
- Maintaining accurate patient and provider information.
- Using appropriate ICD-10, CPT, and HCPCS codes.
- Reviewing modifiers and payer-specific edits.
- Scrubbing claims before submission.
- Monitoring timely filing limits.
- Checking claim status before sending duplicate claims.
- Reviewing EOBs, ERAs, CARCs, and RARCs together.
- Performing regular denial trend and root-cause analysis.
- Monitoring outstanding balances through Accounts Receivable Services.
- Keeping provider enrollment and Credentialing Services current.
Denial Code Categories at a Glance
| Category | Common Codes | Typical Root Cause | Recommended Focus |
| Contractual and Fee Schedule | CO-45, CO-97 | Contract rate or bundling adjustment | Contract review and coding validation |
| Missing Information and Claim Errors | CO-16, CO-4 | Incomplete claim information or coding inconsistency | Claim scrubbing and data validation |
| Medical Necessity and Coverage | CO-50, CO-96, CO-11 | Coverage policy or diagnosis/procedure mismatch | Documentation and coding review |
| Eligibility and Payer Issues | CO-109, CO-31, CO-27 | Wrong payer, inactive policy, member mismatch | Eligibility verification |
| Authorization | CO-197 | Required authorization absent | Prior authorization workflow |
| Timing and Frequency | CO-29, CO-151 | Filing deadline or frequency limitations | Deadline and utilization monitoring |
| Duplicate Billing | CO/OA-18 | Duplicate claim submission | Claim-status monitoring |
| Coordination of Benefits | CO-22, OA-23 | Primary/secondary payer processing | COB verification |
| Patient Responsibility | PR-1, PR-2 | Deductible or coinsurance | Accurate payment posting |
Reducing denials requires collaboration throughout the organization. Front-desk staff, clinical teams, coders, billers, payment posters, and A/R specialists all influence whether a claim is paid correctly on the first submission.
This is why professional Medical Billing Services are closely connected with Revenue Cycle Management Services, Medical Coding Services, Claims Management Services, eligibility verification, prior authorization, payment posting, and denial management.
When these functions operate separately, errors can move downstream unnoticed. When they are connected, the practice has a much better opportunity to catch problems before they affect reimbursement.
Conclusion
Medical billing denial codes provide valuable information about why a payer reduced, denied, or adjusted a healthcare claim. Codes such as CO-16, CO-29, CO-50, CO-97, CO-109, and CO-197 can reveal recurring problems involving missing information, filing deadlines, medical necessity, bundling, payer selection, and prior authorization.
However, not every code represents the same financial situation. CO-45 can reflect an expected contractual adjustment, PR-1 and PR-2 generally represent patient responsibility, and OA-23 reflects prior payer adjudication. CMS specifically explains that the group code helps indicate financial responsibility, while the CARC provides the adjustment reason and the RARC can provide additional detail.
The most effective approach to denial management is prevention combined with structured follow-up.
Healthcare providers should continuously review eligibility verification, authorization processes, clinical documentation, medical coding, claim submission, payment posting, and accounts receivable performance. When denial patterns are analyzed at the root-cause level, they can become a useful tool for improving the entire revenue cycle rather than simply creating additional work for the billing department.
For practices that do not have the internal resources to manage these processes consistently, professional Medical Billing Services, Denial Management Services, Accounts Receivable Services, and complete Revenue Cycle Management Services can provide a more organized approach to cleaner claims and reimbursement management.
Frequently Asked Questions
1. What are the most common medical billing denial codes?
Frequently encountered medical billing denial and adjustment codes include CO-16 for missing or incorrect claim information, CO-29 for timely filing, CO-50 for medical necessity, CO-97 for bundled services, CO-109 for an incorrect payer, and CO-197 for missing authorization. The exact denial mix will differ by specialty, payer, patient population, and billing workflow.
2. What is the difference between a claim denial and a claim rejection?
A rejected claim generally fails an initial validation or submission requirement before full payer adjudication. A denied claim has typically reached payer adjudication but has not been paid as submitted because of coverage, coding, authorization, documentation, or another reimbursement issue. The distinction matters because rejected claims are usually corrected and resubmitted, while denied claims may require a corrected claim, additional documentation, reconsideration, or formal appeal. Current SERP resources consistently identify this as one of the common questions surrounding denial management.
3. What is the difference between a CARC and a RARC?
A Claim Adjustment Reason Code, or CARC, provides the general reason for a payment adjustment. A Remittance Advice Remark Code, or RARC, provides additional information that helps explain the adjustment. For example, CO-16 indicates that information is missing or there is a submission or billing error, but the accompanying RARC can help identify the specific problem that needs correction.
4. What does denial code CO-16 mean?
CO-16 indicates that a claim or service lacks required information or contains a submission or billing error. The billing team should review the associated remark code, identify the incorrect or missing information, correct it, and determine whether a corrected claim or another action is appropriate.
5. What does denial code CO-45 mean?
CO-45 indicates that the billed charge exceeds a fee schedule, maximum allowable amount, or applicable contracted or legislated fee arrangement. It frequently represents a contractual adjustment rather than a complete claim denial. Billing teams should compare the payer’s allowed amount with the contracted rate before deciding whether the adjustment should be posted or disputed.
6. What does denial code CO-97 mean?
CO-97 indicates that payment for the service is included in another service or procedure that has already been adjudicated. Billing teams should review applicable bundling edits, coding rules, documentation, and modifier requirements before deciding whether a correction or appeal is justified.
7. What does denial code CO-29 mean?
CO-29 means the payer’s filing time limit has expired. Practices can reduce these denials by maintaining payer-specific timely filing limits, submitting claims promptly, monitoring claim acceptance, and keeping submission records.
8. What does denial code CO-197 mean?
CO-197 indicates that required precertification, authorization, notification, or pretreatment approval was absent. The best prevention strategy is to verify authorization requirements during scheduling and confirm that the authorization covers the correct service, dates, and other payer requirements before treatment.
9. Can a denied medical claim be resubmitted or appealed?
Many denied claims can be corrected, resubmitted, reconsidered, or appealed, but the appropriate response depends on the denial reason and payer policy. A missing-information denial may simply require a corrected claim. A medical necessity denial may require clinical records and an appeal. An incorrect contractual adjustment may require an underpayment dispute. Billing teams should always review the ERA or EOB, CARC, RARC, payer policy, and filing or appeal deadline before taking action.
10. How can healthcare practices reduce medical billing denials?
Practices can reduce denials by verifying patient eligibility, obtaining required authorizations, maintaining accurate demographics, improving clinical documentation, using accurate medical coding, scrubbing claims before submission, tracking timely filing deadlines, monitoring rejected claims, and analyzing denial trends. A coordinated Revenue Cycle Management Services strategy that connects eligibility verification, Medical Coding Services, Denial Management Services, Accounts Receivable Services, Payment Posting Services, and claims follow-up can help identify problems earlier and prevent recurring billing errors.