CO-50 (Non-Covered Services / Not Medically Necessary)
Contractual Obligation 50 — payer determines the services were not deemed medical necessity by the payer.
1 min read · Last reviewed May 23, 2026
At a glance
- Category
- Denials & Appeals
- Primary sources
- 2
- Workspace handoff
- denial workbench →
Where this comes up
This is denial-workbench territory. A remit posts with a CARC/RARC, the biller decides whether to rebill, appeal, or write off, and the appeal packet has to cite the chart, the order, and the payer's own policy language. Recurring patterns trace back to an upstream workflow gap.
Full definition
What it is in practice
CO-50 is the canonical medical-necessity denial. The CMS Medicare Coverage Database LCDs and NCDs are the typical reference points for an appeal.
How it shows up in your practice
Pair every CO-50 with the relevant LCD / NCD citation in the appeal. Audit ICD-CPT mapping at the front end to prevent the denial.
Sources
- CMS — CARChttps://x12.org/codes/claim-adjustment-reason-codes
- CMS — Medicare Coverage Databasehttps://www.cms.gov/medicare-coverage-database/
Appeal CO-50 denials in the Denial Workbench
Open denial workbench →Related terms
- Denials & AppealsCARC (Claim Adjustment Reason Code)X12-maintained codes communicating why a claim or service line was paid differently than billed.
- PayerLCD (Local Coverage Determination)A MAC-published decision about whether a service is reasonable and necessary in its jurisdiction.
- PayerNCD (National Coverage Determination)A CMS-issued nationwide determination of whether Medicare will cover a particular service.
- CodingMedical NecessityThe standard requiring that services be reasonable and necessary for the diagnosis or treatment of illness or injury or to improve the functioning of a malformed body member.
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Related across the archive
- GlossaryCARC (Claim Adjustment Reason Code)X12-maintained codes communicating why a claim or service line was paid differently than billed.
- GlossaryLCD (Local Coverage Determination)A MAC-published decision about whether a service is reasonable and necessary in its jurisdiction.
- GlossaryMedical NecessityThe standard requiring that services be reasonable and necessary for the diagnosis or treatment of illness or injury or to improve the functioning of a malformed body member.
- GlossaryNCD (National Coverage Determination)A CMS-issued nationwide determination of whether Medicare will cover a particular service.
- GlossaryAppeal LetterThe written request to a payer to reconsider a denied or partially-paid claim.
- ComplianceSMRC Audit Response: The Supplemental Medical Review Contractor WindowAn SMRC letter gives a 45-day documentation window and is shorter-fuse than RAC. Here is the response procedure and how the findings feed back to CMS and the MACs.
- RegulationMLN: Medical Necessity — Local Coverage Determinations (LCDs) and National Coverage Determinations (NCDs)Reference to Medicare's coverage determinations: NCDs are issued by CMS; LCDs are issued by MACs; both define when an item or service is reasonable and necessary.
- BillingHow to Appeal an Insurance Denial: Step-by-Step GuideClaim denied? Step-by-step appeal process with payer deadlines, denial code fixes, appeal letter template, and escalation options.
This glossary entry is a research aid for billing and compliance staff. It does not provide legal, medical, or financial advice and does not replace counsel. References cited link to primary sources at HHS, OCR, CMS, eCFR, NIST, and the relevant payer or industry body.