CO-50 Denial Code: Service denied as not medically necessary by the payer
The payer determined the service was not medically necessary based on its coverage policy. Often tied to a Local Coverage Determination (LCD) or National Coverage Determination (NCD).
- Group code
- CO - Contractual Obligation
- Code type
- CARC
- Billable to patient?
- No - contractual write-off
- Appealable?
- Often, with documentation
- Category
- Medical Necessity
- Common pairing
- N130
CAS*CO*50*125.00On a paper EOB it shows as CO-50.What CO-50 means
CO-50 is a medical-necessity denial: the payer's policy does not consider the service necessary for the reported diagnosis. For Medicare, this usually maps to an LCD or NCD that lists the diagnoses supporting coverage. The most common root cause is a diagnosis that does not meet the policy's covered-indication list, or documentation that does not establish necessity. With supporting documentation, these are frequently overturned on appeal.
Common causes
- The diagnosis billed is not on the payer's list of covered indications for the service (LCD/NCD mismatch).
- Documentation does not establish medical necessity for the service provided.
- A more specific or additional diagnosis that supports necessity was omitted.
- The service is considered screening/experimental under the policy as billed.
How to fix it
- Pull the applicable LCD/NCD or payer medical policy and compare its covered diagnoses to what you billed.
- If a supporting diagnosis is documented but was not coded, submit a corrected claim with the correct, supported diagnosis.
- If necessity is documented, appeal with the chart notes that establish it, citing the policy criteria met.
- If truly not medically necessary and proper advance notice was given, bill per the notice/ABN rules.
How to prevent it
- Check LCD/NCD and payer medical policies at the point of order/scheduling for policy-sensitive services.
- Code diagnoses to the highest specificity supported by the documentation.
- Use ABNs (where applicable) when a service may not meet medical-necessity criteria.
Appeal letter template
Fill in the bracketed fields, attach your supporting documentation, and send through the payer's appeal channel. This is a starting point — adjust to your payer's requirements.
Re: Medical Necessity Appeal (CO-50) - Claim [Claim Number] Patient: [Patient Name] | Member ID: [Member ID] Date(s) of Service: [DOS] | Service: [CPT/HCPCS] | Diagnosis: [ICD-10] To Whom It May Concern: Claim [Claim Number] was denied under CO-50 as not medically necessary. Per [LCD/NCD/Policy Number], coverage is supported for diagnosis [ICD-10], which is documented in the enclosed records. The clinical indication was: [brief clinical rationale]. We request reconsideration and payment. Supporting documentation (office/procedure notes, relevant results) is enclosed. Sincerely, [Your Name], [Practice Name] | [Phone] | [NPI/TIN]