CO-50: denied as not medically necessary

Claim adjustment reason code 50 says the service is non-covered because the payer does not consider it a medical necessity. The group code CO (contractual obligation) means the amount is the provider's responsibility: you can't bill the patient for it, unless the patient signed a valid Advance Beneficiary Notice before the service (see section 4).

In practice, on a Medicare claim it usually means the diagnosis on the claim did not support the procedure under the coverage policy that applies to you.

Medicare publishes coverage rules in two forms. A National Coverage Determination (NCD) applies everywhere. A Local Coverage Determination (LCD) is published by the contractor for one region, usually with a billing and coding article listing the diagnoses that support each procedure. The common causes of a CO-50 are:

• The diagnosis isn't on the covered list. For example, a symptom code billed where the policy lists only specific conditions.
• The diagnosis isn't specific enough. The covered list names a more specific code than the one billed, even though the note supports it.
• The policy explicitly excludes the diagnosis for that procedure.
• A frequency or utilisation limit in the policy was exceeded.
• The wrong region's rules were assumed. A policy from another contractor doesn't bind you, and yours may differ.

• Know your contractor. Your clinic's state decides which contractor's local policies apply. Find yours with the contractor lookup.
• Check the diagnosis against the policy before the claim goes out, for every procedure that has an NCD or LCD in your region.
• Code to the most specific diagnosis the note supports. Many "not covered" diagnoses are really "not specific enough".
• Make sure the documentation shows why the service was needed. A covered diagnosis doesn't help if the note doesn't support it.

If you expect Medicare to deny a service as not medically necessary, you can give the patient an Advance Beneficiary Notice of Non-coverage (ABN) before the service. With a valid, signed ABN, you add the GA modifier, and if Medicare denies the service the patient can be billed for it.

The GZ modifier tells Medicare you expect a denial but did not obtain an ABN; the patient can't be billed in that case. An ABN only helps if it is given before the service, which is why the check is most useful early.

• Read the policy that applied. Find the LCD or NCD and its coding article for the procedure, for your contractor.
• If a more specific, covered diagnosis is documented, the fix is usually a correction rather than an argument. Follow your contractor's process for reopening or correcting the claim.
• If the diagnosis was right and the service was necessary, request a redetermination (Medicare's first appeal level) within 120 days of receiving the initial determination, with the clinical note that shows why.
• If the policy explicitly excludes the diagnosis, an appeal needs strong clinical evidence. Consider whether the claim should have been billed, and whether an ABN should be used next time.

• CO-11: the diagnosis is inconsistent with the procedure.
• CO-167: the diagnosis is not covered.

This guide is general information, not legal or billing advice. Always check the current policy for your contractor and your payer's own rules.