How do I work a CO-50 denial?
Quick Answer
CO-50 means the payer determined the service was not medically necessary. Review the payer's coverage policy (LCD/NCD), assess whether your clinical documentation supports medical necessity, and either appeal with supporting documentation or issue an ABN and bill the patient.
Step-by-Step Instructions
Review the denial and the payer's coverage policy
CO-50 means the payer does not consider the service medically necessary. Check the payer's Local Coverage Determination (LCD) or National Coverage Determination (NCD) for the specific CPT code. These policies define what diagnoses and documentation are required for coverage.
Assess your clinical documentation
Review the patient's medical records. Does the documentation clearly support medical necessity? Look for: the diagnosis code matches the LCD, the frequency/quantity is within policy limits, and the clinical notes justify the service. If documentation is weak, an appeal is unlikely to succeed.
Determine your course of action
If the documentation supports medical necessity, file an appeal with clinical records. If the documentation is insufficient, write off the balance (or bill the patient if an ABN was signed). Do not appeal without strong supporting documentation — weak appeals waste time.
File a medical necessity appeal (if warranted)
Submit a formal appeal with a cover letter explaining why the service was medically necessary, the clinical notes, relevant payer policy citations, and any specialist letters or second opinions. For Medicare, follow the 5-level appeal process starting with Redetermination.
Issue an ABN for future services (Medicare)
If you know a service will likely be denied as not medically necessary for a Medicare patient, issue an Advance Beneficiary Notice (ABN) before the service. This allows you to bill the patient if Medicare denies. Without the ABN, you cannot bill the patient for a Medicare denial.
Track and learn from the denial
Document the denial, the appeal outcome, and the root cause. If the denial was due to a diagnosis code not covered by the LCD, update your coding protocols. If documentation was insufficient, provide feedback to the clinical team to prevent future CO-50 denials.
Common Mistakes to Avoid
Appealing without strong clinical documentation — weak appeals waste time and rarely succeed.
Not checking the LCD/NCD before billing — you can prevent CO-50 denials by verifying coverage criteria upfront.
Billing the Medicare patient without an ABN — you cannot bill the patient for a medical necessity denial without prior notice.
Not addressing the root cause — if your documentation is consistently weak, appeals will not fix the underlying problem.
Confusing CO-50 with CO-151 — CO-50 is medical necessity; CO-151 is utilization (frequency limits exceeded). The appeal strategies differ.