10 Medical Billing Denial Codes That Affect Your Revenue

Medical billing denials can be a major cause of healthcare revenue. It will lead to lost income and increased administration workload. As a healthcare professional and medical biller, you should understand the standard denial codes because they ensure improving claim approval rates and maintaining a steady cash flow.

In this blog post, we have shared the 10 medical billing denial codes that frequently impact healthcare providers, their causes, and solutions to reduce claim rejections.

10 Medical Billing Denial Codes that Affect Your Revenue

1. CO-4 – Missing Modifier

This code indicates that a required modifier is missing or the procedure code is inconsistent with the modifier used. Modifiers provide additional information about the performed service. If the modifiers or absent or misused, it can lead to claim denials. 

CO-4 denial code occurs if the medical billing or healthcare providers fail to include necessary modifiers or use incorrect ones that do not align with the billed procedure. To solve this, 

• Review the claim to identify missing or incorrect modifiers before submitting it to the payers.
• Correct the modifier usage and resubmit the claim.​
• Implement regular training for coding staff to ensure proper modifier application.

2. CO-11 – Diagnostic Coding Error

This denial occurs when the diagnosis code submitted does not match the procedure performed or is deemed inappropriate. 

Accurate diagnosis codes are essential to justify the medical necessity of services rendered. If the diagnosis codes are Incorrect or mismatched and do not support the billed services, this denial code will cause. To prevent this, healthcare providers and billing teams should:

• Verify the accuracy of diagnosis codes about the provided services.
• Correct any discrepancies and resubmit the claim.
• Ensure coding staff are up-to-date with current coding standards and guidelines.

3. CO-15 – Missing or Invalid Authorization Number

This code signifies that the claim lacks a necessary authorization number or contains an invalid one. Certain procedures require prior authorization to ensure coverage. 

Failure to obtain prior authorization or inclusion of an incorrect authorization number in the claim. To prevent this from happening, you should:

• Confirm whether prior authorization was obtained for the service.​
• Ensure the correct authorization number is included in the claim.​
• Establish a verification process to confirm authorizations before claim submission.

4. CO-16 – Missing Information

This denial indicates that the claim lacks necessary information or contains missing/incorrect modifiers, making it unprocessable. Incomplete claim forms, missing patient information, or absent required documentation are the major cause of this denial code. 

The billing team should make sure to review the claim for completeness and accuracy. Provide any missing information or documentation. Implement a checklist to ensure all required fields and attachments are included before submission.

5. CO-18 – Duplicate Claim or Service

This code is assigned when a claim is identified as a duplicate of one already submitted and processed. Submitting the same claim multiple times without indicating it as a corrected or follow-up claim. 

To solve this denial code:

• Verify claim status before resubmission to avoid duplicates.​
• Use appropriate coding to indicate corrected claims.
• Establish protocols to track submitted claims and their statuses.

Related: How Medical Billing Audits Can Prevent Revenue Leakage & Increase Profitability

6. CO-22 – Coordination of Benefits Error

This denial occurs when there is confusion about the order of payers, especially when multiple insurance coverages exist. Incorrect identification of primary and secondary payers or lack of updated insurance information. Follow the below practices to make sure to prevent this denial code:

• Collect and verify all insurance information from patients.​
• Determine the correct order of payers before claim submission.​
• Update patient records regularly to reflect current insurance coverage.

7. CO-27 – Insurance Coverage Terminated

This code indicates that the patient’s insurance coverage was not active on the date of service. This is majorly caused by services rendered after the patient’s insurance policy has expired or terminated. To solve this verify patient insurance eligibility before providing services.​

Confirm coverage dates and any recent changes to the policy.​ Then, Educate patients on the importance of maintaining active insurance coverage.

8. CO-29 – Late Submission

The CO-29 denial code is issued when a claim is submitted after the payer’s designated filing deadline. Claims submitted past the insurer’s allowable timeframe, which varies by payer. To solve this:

• Review payer-specific submission deadlines to ensure compliance.
• Establish a streamlined workflow for timely claim submission.
• Implement automated reminders to track and submit claims within the required timeframe.

9. CO-45 – Charges Exceed Fee Schedule

This denial occurs when the billed amount exceeds the allowed amount per the payer’s fee schedule. The major cause is when providers charge above the contracted rate or misalignment with the insurer’s allowable reimbursement rates. 

To prevent this denial, verify the payer’s fee schedule and adjust billing accordingly. Then ensure claims are coded correctly to reflect contractually agreed rates. Conduct periodic audits to align charge entries with payer agreements.

10. CO-97 – Service Not Covered or Included in Another Service

This denial is used when the billed service is not covered under the patient’s insurance policy or is considered part of a bundled payment. The cause of this is when the service is excluded from the patient’s benefits, or it is considered an inclusive component of another billed procedure. 

To solve this, medical billers and healthcare providers need to:

• Verify insurance coverage details before rendering services.
• Appeal denials with supporting documentation if the service was medically necessary.
• Educate patients about their coverage limitations and potential out-of-pocket costs.

Medical billing denials can be a major problem for healthcare providers. Because it leads to revenue losses and creates inefficiency in billing operations. If the billing team understands the common denial codes in billing, they can take proactive measures to minimize claim rejections.

Related: Top 10 Medical Billing Companies in the US for 2025

Optimize Your Medical Billing with CapMinds Service

Managing medical billing efficiently is crucial for a financially healthy practice, but dealing with claims, coding, denials, and compliance can be overwhelming. CapMinds is here to help you!

Our end-to-end medical billing services ensure seamless claim processing, higher reimbursements, and reduced denials, so you can focus on delivering quality patient care.

Why Choose CapMinds for Medical Billing?

• Faster Claims Processing – Minimize delays and boost revenue.
• Error-Free Medical Coding – Reduce claim rejections with accurate CPT & ICD coding.
• Denial Management & Appeals – Recover lost revenue efficiently.
• Compliance & HIPAA Security – Stay aligned with industry regulations.
• Dedicated Client Manager – Personalized support for your practice’s needs.
• 24/7 Billing Support – Expert assistance whenever you need it.

With CapMinds, you get a trusted medical billing partner that enhances cash flow, improves operational efficiency, and optimizes revenue cycles. 

Let us handle your billing complexities, so you can focus on growing your practice!

Contact CapMinds today and experience hassle-free medical billing!