Key Takeaways:

• Denial codes decode the “why” behind unpaid claims.

• Rejections happen before processing; denials happen after.

• Decoding denial codes correctly accelerates reimbursement, strengthens appeals, clarifies financial responsibility, and improves the patient billing experience.
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• Most denials are preventable with upfront checks and clean claims.

• AI can shift denial management from reactive fixes to proactive prevention.

No matter how efficient your revenue cycle team is, claim denials can drain a lot of your team’s time, delay payments, and cloud accountability.

They show up with cryptic codes, vague reasons, and leave you asking: “Do we fix this, appeal it, or just write it off?”

But most denials come with standardized codes that, if read correctly, tell you exactly what went wrong and what to do next. 

That’s why we created this guide—to help you make sense of the common claim denial codes you’ll see in your ERAs and EOBs. We’ll break down what these denial codes actually mean, why they show up, and what to do when they land in your workflow.

What Are Medical Claim Denial Codes?

Medical claim denial codes are standardized codes used by insurance payers to explain why a healthcare claim was denied, reduced, or not paid as submitted. These codes help providers, billing teams, and revenue cycle staff identify the reason for the denial and determine whether the claim should be corrected, appealed, or written off. These codes are included in the payer’s Electronic Remittance Advice (ERA) or Explanation of Benefits (EOB) after the claim is processed.

In medical billing, denial codes are typically communicated through two code systems:

• CARC (Claim Adjustment Reason Code): Specific reason the claim was adjusted or denied
• RARC (Remittance Advice Remark Code): Extra context or instructions from the payer

Each of these codes are prefixed with Group Code (CO, PR, OA, PI), which tells who is responsible for the adjustment.

Once you receive the remittance letter, you need to decide whether to:

• Correct and resubmit
• Appeal with documentation
• Or bill the patient

How Does Claim Denial Differ From Claim Rejection?

A rejection happens before adjudication during front-end validation at the clearinghouse or payer intake. Unlike denied cases, you don’t get denial codes or an ERA. You see a rejection notice that points to data or format errors to fix. You correct the error and resubmit.

Let us explain this with an example:

Say you submit CPT 70551 (MRI) for a patient. Here’s what happens when the claim is rejected vs. denied:

Why Are Denial Codes Important?

When you can read and decode denial codes, you turn a vague “no” into a clear plan that moves money faster within your RCM workflow. 

Here’s what you get for reading and decoding denial codes correctly:

• Faster reimbursement: You see the exact reason and the required fix, so you correct it once and move the claim to payment sooner.
• Clean responsibility split: Group Codes show whether to adjust as contractual, appeal to the payer, or bill the patient compliantly.
• Stronger appeals: RARCs often tell you what evidence or policy to include, so your appeal packets land the first time.
• Better prioritization: You can triage work by “quick correction” vs “full appeal” vs “re-bill,” which lowers touches per claim.
• Smoother patient experience: Correct PR vs CO decisions prevent surprise bills and unnecessary write-offs.
• Operational visibility: Standardized codes feed dashboards and automation, so you can monitor denial rate, avoidable denial mix, and time to cash.

How Does the Claim Denial Communication Process Work

Medical claim denials are typically communicated after a payer reviews and adjudicates a submitted claim.

Here’s how the denial communication process usually works:

1. Provider Submits the Claim

The healthcare provider sends a claim to the payer with procedure codes, diagnosis codes, patient information, and supporting documentation.

2. Payer Reviews the Claim

The insurance payer evaluates the claim for:

• eligibility
• coverage rules
• medical necessity
• authorization requirements
• coding accuracy
• timely filing compliance

3. Claim Is Approved, Adjusted, or Denied

If the payer identifies an issue, they assign one or more CARC and RARC codes explaining the denial or payment adjustment.

4. Provider Receives ERA or EOB

The denial information is communicated back through:

• ERA (Electronic Remittance Advice) for electronic billing workflows
• EOB (Explanation of Benefits) for payment summaries and patient-facing communication

5. Billing Team Reviews and Resolves the Denial

Revenue cycle teams then determine whether the denial should be:

• corrected and resubmitted
• appealed with documentation
• transferred to patient responsibility
• written off according to payer policy

Common Denial Codes in Medical Billing

Whether you're chasing down a $30 copay or a $3,000 denial, understanding the code behind it is the first step. 

Here's a breakdown of some common denial codes and the real-world situations where they typically show up.

CARC (Claim Adjustment Reason Codes) explain the primary reason a medical claim was denied, adjusted, or reduced by the payer. RARC (Remittance Advice Remark Codes) provide additional details or instructions to help providers understand the denial and determine the next steps for resolution.

Claim Adjustment Reason Code

CARCs are the standardized reasons payers use to explain why a claim line was paid, reduced, or denied differently than you billed. They’re numeric (e.g., 16, 29, 45, 97) and appear on your ERA/EOB after adjudication. 

On ERAs, each CARC sits inside an adjustment entry with a Group Code that assigns financial responsibility (provider write-off, patient liability, other adjustment, or payer-initiated reduction).

Here are some common CARC codes found in denied claims:

Remittance Advice Remark Code

RARCs are short, standardized messages the payer puts on your ERA/EOB to add detail about a payment adjustment or to share general “alert” information about how the remittance was processed. They either supplement a CARC or appear as informational messages with no dollar change.

But, RARC codes don’t always appear on the EOB/ERA. Some adjusted lines include only Group Code and CARC. RARCs are used only if the payer needs to add detail or an alert.

Here are the common RARC codes you’ll see and what they each mean:

Top 10 Medical Billing Denial Codes

CO-16: Missing or Invalid Information

This denial means required claim details are incomplete or inaccurate. Common causes include missing modifiers, invalid diagnosis codes, or incorrect patient data. Resolve it by reviewing the claim, correcting errors, and resubmitting promptly. Prevent future denials through claim scrubbing and staff training. This denial is usually appealable if supporting documentation is available.

CO-18: Duplicate Claim

CO-18 indicates the payer believes the claim was already processed. It often happens because of accidental resubmissions or system errors. Verify claim history before rebilling and submit corrected claims only when necessary. Prevent duplicates with proper claim tracking systems. Appeals are possible if the original claim was not actually paid.

CO-22: Coordination of Benefits Issue

This code appears when multiple insurers are involved and payment responsibility is unclear. Incorrect primary insurance details are the most common cause. Confirm insurance order with the patient and resubmit corrected claims. Prevent issues by verifying benefits before service. These denials are appealable with updated COB information.

CO-27: Coverage Terminated

This denial means the patient’s insurance coverage was inactive on the service date. Resolve it by confirming eligibility or billing the correct payer. Eligibility verification before appointments helps prevent this issue. Appeals are only possible if coverage was active in error.

CO-29: Timely Filing Limit Exceeded

This denial occurs when a claim is submitted after the payer’s filing deadline. Common causes include delayed documentation, billing backlogs, or incorrect insurance information. To resolve it, verify the payer’s filing policy and submit an appeal with proof of timely filing if available. Prevent this denial by tracking claim deadlines and automating claim submission workflows. This denial is sometimes appealable when evidence shows the claim was originally filed on time.

CO-45: Charges Exceed Fee Schedule

CO-45 means the billed amount is higher than the payer’s allowed reimbursement rate. It commonly happens due to contractual adjustments or outdated fee schedules. Resolve it by reviewing payer contracts and adjusting the balance appropriately. Prevent future denials by maintaining updated payer fee schedules and verifying contracted rates regularly. This denial is generally not appealable unless the reimbursement was calculated incorrectly.

CO-50: Medical Necessity Not Established

This denial indicates the payer believes the service provided was not medically necessary. Common causes include insufficient documentation, incorrect coding, or services not meeting payer guidelines. Resolve it by submitting supporting clinical records and a detailed appeal. Prevent denials by ensuring documentation clearly supports treatment necessity before claim submission. This denial is often appealable with strong medical evidence.

CO-96: Non-Covered Charges

CO-96 means the service is not covered under the patient’s insurance plan. It may occur because of plan exclusions, cosmetic procedures, or benefit limitations. To resolve it, verify benefits and bill the patient if appropriate. Prevent this denial by confirming coverage before treatment and informing patients of financial responsibility. Appeals are only possible if the service should have been covered under the policy.

CO-109: Wrong Payer

This denial occurs when the claim is sent to the incorrect insurance company. Common causes include outdated insurance details or COB errors. Resolve it by identifying the correct payer and resubmitting the claim. Prevent future denials through eligibility verification at every visit. This denial is appealable only if the payer processed the claim incorrectly.

CO-197: Authorization/Referral Missing

CO-197 indicates required prior authorization or referral was not obtained before services were provided. Common causes include administrative oversight or incomplete referral documentation. Resolve it by obtaining retroactive authorization when possible and resubmitting the claim. Prevent denials with pre-service authorization checks and workflow reminders. This denial may be appealable depending on payer policies and clinical urgency.

How Healthcare Providers Can Reduce Claim Denials

Healthcare providers can significantly reduce claim denials by improving front-end verification, strengthening documentation processes, and using technology-driven denial prevention strategies. A proactive revenue cycle management approach helps providers improve reimbursement rates and reduce administrative costs.

Eligibility Checks

Insurance eligibility verification is one of the most effective ways to prevent denials. Verifying patient coverage, policy status, copays, deductibles, and payer requirements before appointments helps avoid issues such as inactive coverage or incorrect payer submissions. Automated eligibility tools can streamline this process and reduce manual errors.

Authorization Workflows

Many denials occur because prior authorizations or referrals are missing. Providers can reduce these denials by implementing standardized authorization workflows that track approval requirements before services are performed. Automated reminders and centralized authorization teams help ensure compliance with payer rules and avoid delays in claim submission.

Coding Audits

Accurate medical coding is essential for clean claims. Regular coding audits help identify errors in CPT, ICD-10, and HCPCS codes that may trigger denials. Audits also ensure documentation supports medical necessity and payer guidelines. Ongoing coder education and compliance reviews further reduce coding-related denials.

AI-Assisted Denial Management

Artificial intelligence tools can identify denial patterns, predict high-risk claims, and automate claim corrections before submission. AI-assisted denial management improves claim accuracy, speeds up appeals, and reduces repetitive manual work. Predictive analytics also help billing teams prioritize claims that are most likely to be denied.

Analytics and Reporting

Revenue cycle analytics provide visibility into denial trends, payer behavior, and operational inefficiencies. Monitoring denial rates, root causes, and reimbursement timelines helps providers make data-driven improvements. Regular reporting enables healthcare organizations to address recurring denial issues and optimize financial performance.

What Does An AI-Assisted Denial Prevention and Management Look Like?

Denial management shouldn’t be just about fixing claims after they’re denied. Preventing the denials in the first place matters just as much, and even more, since most of the denials are avoidable.

The reality is that most RCM teams manage denials manually, one claim at a time. 

But, with AI built into the right moments, i.e., before submission, during follow-up, and when preparing appeals, you can shift from reactive cleanup to proactive prevention. 

Here’s what proactive denial prevention and management with CombineHealth’s AI agents looks like in practice:

1. Jessica (our AI scribing agent) transcribes clinician notes in real-time and creates standardized documents to be passed for coding.
2. Amy (our AI coding agent) takes over by assigning the ICD, CPT, and E/M codes, providing a line-by-line rationale, and updating codes into the EHR. She even spots documentation gaps in real-time.
3. Mark (our AI billing agent) then navigates payer portals and aggregators to perform patient eligibility checks. He also applies payor-specific billing SOPs, validates codes & modifiers, and prepares charges for claim submission.
4. Upon denial, Adam (our AI denial management agent) works with the payor portals, payor chatbots, and aggregators like Availity for claim status checks and makes follow-up calls.
5. Finally, Rachel (our AI appeal agent) drafts clear, payer-specific appeal letters.
6. But before closing the loop, Mark continuously learns from prior denial patterns for smarter future actions.

FAQs

What is the purpose of a denial code?

A denial code explains why a payer didn’t pay a claim as billed. It helps providers identify the issue (like missing info, medical necessity, or coverage problems), so they can correct, appeal, or adjust the claim accordingly.

What does “denial upheld” mean?

“Denial upheld” means the payer reviewed your appeal but decided not to reverse the denial. The claim remains unpaid unless further action (like a second-level appeal) is taken.

What is a COB denial code in medical billing?

COB (Coordination of Benefits) denial codes indicate the claim should’ve gone to another payer first. These denials happen when primary and secondary payer info is missing, outdated, or mismatched.

How do you handle claim denials?

Start by reviewing the denial code and Group Code. Then decide whether to correct and resubmit, appeal with documentation, or adjust the claim per policy. Prioritize high-dollar or easily fixable denials first.

How to prevent claim denials?

Use pre-bill edits, verify eligibility and authorization, apply correct coding, and stay current on payer rules. Trend denial codes regularly to fix upstream issues before claims go out.

What does CO-197 mean?

CO-197 means the payer denied the claim because required authorization, precertification, or referral approval was missing or invalid.

What is the most common denial code in medical billing?

CO-16 is one of the most common denial codes in medical billing and usually indicates missing, incomplete, or invalid claim information.

How do you interpret medical claim denial codes?

To interpret a denial code, billing teams review the CARC and RARC codes included in the payer’s ERA or EOB to identify the denial reason, determine root cause, and decide whether to correct, resubmit, or appeal the claim.

What are CARC and RARC codes?

CARC codes explain the primary reason for a claim denial or adjustment, while RARC codes provide additional details or instructions to help providers resolve the issue.

Which denial codes are usually preventable?

Many denials are preventable, including eligibility issues, missing authorization, coding errors, duplicate claims, and incomplete patient information. Strong front-end workflows and claim scrubbing can significantly reduce these denials.