The 10 Most Common Claim Denial Codes and How to Fix Them
Claim denials cost the average medical practice 3-5% of net revenue. But the vast majority of denials are caused by the same handful of reason codes, and most of them are preventable. Understanding these codes is the first step to reducing your denial rate and recovering lost revenue.
Here are the 10 most common Claim Adjustment Reason Codes (CARCs), what causes them, and how to resolve and prevent each one.
1. CO-16: Missing Information Needed for Adjudication
What it means: The claim is missing data the payer needs to process it. This is the single most common denial code and is often a catch-all for various missing data elements.
Common causes: Missing referring provider NPI, invalid place of service code, missing taxonomy code, incomplete patient demographics, or required attachments not submitted.
How to fix it: Check the accompanying RARC (Remittance Advice Remark Code) to identify exactly what is missing. The RARC will tell you whether it is a missing NPI, an invalid date, or a required document. Correct the issue and resubmit.
How to prevent it: Implement pre-submission claim scrubbing that validates all required fields against payer-specific rules before the claim goes out the door. Learn more about CO-16.
2. CO-15: Authorization Required but Not Obtained
What it means: The service required prior authorization, and no valid authorization was on file when the claim was submitted.
Common causes: PA was never requested, PA was obtained but expired before the date of service, authorization number was not included on the claim, or the authorized CPT code does not match the billed code.
How to fix it: Check if a valid authorization exists that was simply not attached to the claim. If so, add the auth number and resubmit. If no authorization exists, submit a retro-authorization request if the payer allows it. If retro-auth is denied, appeal with clinical documentation.
How to prevent it: Check PA requirements at the time of scheduling, not at the time of billing. Automate PA status tracking so expiring authorizations are flagged before the date of service. Learn more about CO-15.
3. PR-1: Deductible Amount
What it means: This is not technically a denial. The claim was processed correctly, and the patient owes the deductible amount. The service is covered, but the patient has not yet met their annual deductible.
Common causes: Patient has a high-deductible health plan, deductible just reset at the start of the plan year, or the practice did not check deductible status before the visit.
How to fix it: Bill the patient for the deductible amount. This is legitimate patient responsibility.
How to prevent it: Run eligibility and benefit verification before every visit so you know the patient's deductible status. Collect estimated patient responsibility at time of service. Learn more about PR-1.
4. CO-11: Diagnosis Inconsistent with Procedure
What it means: The ICD-10 diagnosis code submitted does not support the medical necessity of the procedure billed. The payer does not believe the diagnosis justifies the service.
Common causes: Wrong ICD-10 code selected, unspecified diagnosis used when a specific code was required, missing laterality, or the diagnosis simply does not match the procedure per the payer's coverage policy.
How to fix it: Review the medical record and select the most specific, accurate diagnosis code that supports the procedure. Check the payer's LCD/NCD for covered diagnoses. Resubmit with the corrected code.
How to prevent it: Implement diagnosis-procedure crosswalk validation in your billing system. Code to the highest specificity. Train providers on documentation that supports procedure-diagnosis linkage. Learn more about CO-11.
5. CO-4: Procedure Code Inconsistent with Modifier
What it means: The modifier appended to the CPT code is not valid for that code, or a required modifier is missing.
Common causes: Incorrect modifier used, modifier required but not included, bilateral modifier on a procedure that cannot be bilateral, or incorrect use of modifier 59.
How to fix it: Review the CPT code and verify the correct modifier. Consult payer-specific modifier guidelines. Correct and resubmit.
How to prevent it: Use coding validation tools that check modifier-code compatibility before submission. Keep CPT code sets updated annually. Learn more about CO-4.
6. CO-45: Charges Exceed Fee Schedule
What it means: Your billed charges are higher than the payer's contracted or allowed amount. The payer is adjusting to their fee schedule rate. This is usually a normal contractual adjustment, not a problem to fix.
Common causes: Standard fee schedule adjustment for in-network claims. Your billed charges should always be higher than the contracted rate.
How to fix it: For in-network claims, write off the contractual adjustment. Do not balance bill the patient. If the allowed amount is lower than your contracted rate, appeal with a copy of your contract.
How to prevent it: This is generally expected. Review your fee schedules annually during contract negotiations to ensure fair reimbursement. Learn more about CO-45.
7. CO-50: Non-Covered Service (Medical Necessity)
What it means: The payer determined the service is not medically necessary based on the diagnosis and clinical information submitted.
Common causes: Diagnosis does not meet LCD/NCD criteria, frequency limits exceeded, conservative treatment not attempted first, or missing clinical documentation.
How to fix it: Request a peer-to-peer review. File a formal appeal with a detailed letter of medical necessity and supporting clinical documentation.
How to prevent it: Check coverage criteria before performing the service. Ensure documentation clearly supports necessity. Obtain PA for services flagged for medical necessity review. Learn more about CO-50.
8. CO-18: Duplicate Claim
What it means: This claim has already been submitted and processed. The payer sees it as a duplicate.
Common causes: Accidental resubmission, corrected claim sent without proper frequency code, or different staff submitted the same claim.
How to fix it: Verify the original claim was paid. If this is a corrected claim, resubmit with frequency code 7 (replacement) and the original claim number.
How to prevent it: Track claim submission status. Use proper frequency codes for corrected claims. Implement duplicate detection in your billing workflow. Learn more about CO-18.
9. CO-29: Timely Filing Limit Exceeded
What it means: The claim was not submitted within the payer's filing deadline. Most payers require submission within 90-365 days.
Common causes: Billing backlog, claim sent to wrong payer initially, waiting on primary payer delayed secondary filing, or staff turnover caused processing gaps.
How to fix it: If you have proof of timely submission (clearinghouse confirmation), appeal immediately. If delayed due to COB, provide documentation of the primary payer timeline.
How to prevent it: Submit all claims within 48 hours. Run weekly aging reports to catch claims approaching deadlines. Set automated alerts at 60, 90, and 120 days. Learn more about CO-29.
10. CO-197: Precertification/Authorization Absent
What it means: Very similar to CO-15. A required precertification, authorization, or notification was not obtained. This code specifically references the absence of the precertification process.
Common causes: PA was not requested, notification was required but not provided, or payer added new PA requirements that the practice was not aware of.
How to fix it: Submit a retro-authorization if the payer allows it. If the service was emergent, appeal with documentation of the emergency.
How to prevent it: Automate PA requirement checks for every scheduled service. Subscribe to payer policy updates. Learn more about CO-197.
The Pattern: Most Denials Are Preventable
Looking at this list, a clear pattern emerges. The top denial codes fall into a few preventable categories:
- Missing information (CO-16, CO-252) -- solvable with pre-submission validation
- Authorization failures (CO-15, CO-197) -- solvable with automated PA tracking
- Coding errors (CO-4, CO-11) -- solvable with code validation tools
- Eligibility issues (CO-27, CO-96) -- solvable with real-time eligibility checking
A well-designed workflow that verifies eligibility, checks PA requirements, and validates claims before submission can prevent 80% or more of all denials.
If you want to see how this works in practice, schedule a demo of Greenlight Medical to see automated PA and eligibility verification in action.