What are common denial codes in billing?

Common denial codes in medical billing are standardized Claim Adjustment Reason Codes (CARCs) paired with group prefixes like CO (Contractual Obligation) that explain why an insurance claim was reduced or rejected.

💡 Most Common Denial Codes and Solutions

• 📌 CO-16: Missing or Incomplete Information
  • Meaning: Essential data like an NPI or diagnosis is absent.
  • Fix: Add missing details and resubmit the corrected claim.
• 📌 CO-18: Duplicate Claim/Service
  • Meaning: The exact same service was already billed.
  • Fix: Confirm if it's a true duplicate or appeal as a corrected claim.
• 📌 CO-22: Coordination of Benefits (COB) Issue
  • Meaning: Another insurer needs to be billed first.
  • Fix: Update primary insurance details and rebill the correct payer.
• 📌 CO-29: Timely Filing Limit Exceeded
  • Meaning: The claim was submitted past the insurer's deadline.
  • Fix: Provide proof of timely submission or initial rejection appeal.
• 📌 CO-50 / CO-197: Medical Necessity / Authorization Absent
  • Meaning: Lacks prior authorization or clinical support for the service.
  • Fix: Submit medical records or retroactive authorization documentation.
• 📌 CO-97: Bundled Service
  • Meaning: Procedure code is already included in another billed service.
  • Fix: Review bundling rules or apply appropriate CPT modifiers.
• 📌 CO-109: Incorrect Patient Eligibility
  • Meaning: Insurance was inactive on the date of service.
  • Fix: Verify active coverage status prior to patient intake.

The top 10 denial codes in medical billing represent the most frequent Claim Adjustment Reason Codes (CARCs) that cause claim rejections or payment reductions across insurance payers.

Here are the 10 most common denial codes and what they mean:

• CO-16 – Claim Lacks Information: The claim is missing essential data, such as a modifier, referring provider NPI, or valid demographics.
• CO-18 – Duplicate Claim/Service: The same service was submitted more than once for the same date before the first claim finished processing.
• CO-22 – Coordination of Benefits (COB) Issue: Another insurance plan is primary, and the claim was billed to the wrong payer first.
• CO-29 – Timely Filing Limit Exceeded: The claim was submitted after the payer’s strict submission deadline.
• CO-45 – Charge Exceeds Fee Schedule: The billed amount is higher than the contracted or allowable rate set by the insurance company.
• CO-50 – Not Deemed Medical Necessity: The diagnosis code provided does not support the procedure per the payer's local or national coverage rules.
• CO-96 – Non-Covered Charge(s): The billed service falls completely outside the patient's covered insurance benefits.
• CO-97 – Service Included in Another Procedure (Bundling): The procedure cost was already bundled into the allowance of a primary service billed on the same day.
• CO-109 – Claim Not Covered by This Payer / Incorrect Eligibility: The patient's policy was inactive on the date of service, or the claim went to the wrong contractor/crossover payer.
• CO-197 – Precertification/Authorization Absent: The required prior authorization was missing, expired, or failed to match the specific service billed.

Five common Current Procedural Terminology (CPT) codes used in routine medical practice include office visits, lab tests, and basic evaluations.

Common CPT Codes

• 99213: Office or other outpatient visit for the evaluation and management of an established patient, typically lasting 20 to 29 minutes.
• 99214: Office or other outpatient visit for an established patient, typically lasting 30 to 39 minutes with a moderate level of medical decision-making.
• 36415: Routine venipuncture, meaning drawing blood from a vein using a needle.
• 93000: Routine electrocardiogram (ECG/EKG) tracing with at least 12 leads, including the interpretation and report.
• 71045: Chest X-ray, single view.

A CO-252 denial code means an insurance company has paused a medical claim because it is missing required supporting documents or attachments.

What It Means

• The official description states: "An attachment/other documentation is required to adjudicate this claim/service".
• The "CO" prefix stands for Contractual Obligation, which means the provider absorbs the financial delay and cannot bill the patient for the missing paperwork issue.
• The claim is not completely rejected; it is just waiting for more proof.

Common Causes

• Missing clinical notes, progress notes, or operative reports.
• Omitted lab results, pathology reports, or imaging scans.
• Lacking proof of prior authorization or medical necessity.

How to Fix It

• Check the accompanying Remittance Advice Remark Code (RARC) to see what specific file the insurer wants.
• Gather the needed medical records or i-med claims co 252 denial code in medical billing guidance.
• Send the missing documents to the insurance payer through their portal, fax, or electronic attachment.

A CO 27 denial is a medical billing rejection meaning the insurance company refused to pay because the service date occurred after the patient's coverage had expired or terminated.

What the Code Means

• CO: Stands for Contractual Obligation, indicating the payer adjusts or denies the amount based on contract terms, making it initially uncollectible from the patient under that specific policy status.
• 27: The Claim Adjustment Reason Code (CARC) specifying "Expenses Incurred After Coverage Terminated".
• Conversion to PR 27: If the provider cannot recover funds from the insurer and shifts the bill due to lack of other coverage, the code often converts to a PR 27 (Patient Responsibility), meaning the patient may owe the balance out-of-pocket.

Common Causes

• Skipping Eligibility Checks: Failing to verify active insurance coverage before rendering the service.
• Outdated Patient Records: The provider billing an old insurance plan after the patient switched policies or lost job-based coverage.
• Delayed Claim Submissions: Sending the claim past the policy termination date or outside timely filing limits while using inactive details.

How to Fix It

• Verify Dates: Contact the payer to check the exact policy effective and termination dates.
• Find Secondary Insurance: Ask the patient if they had active secondary coverage during the date of service.
• Bill the Patient: If no other active coverage exists and the service was genuinely delivered post-termination, update the ledger to self-pay/patient responsibility.