CO-50 means the payer decided the service was not medically necessary under its coverage policy, so it will not pay. The denial is about the clinical case, not the coding. Recovery depends on showing that this patient met the payer's written criteria, through the record, the policy itself and, when needed, a peer-to-peer review.
CO-50: "These are non-covered services because this is not deemed a 'medical necessity' by the payer."
The two codes are often confused because both involve a payer's judgment about the record. They point to different questions, and the appeal is built differently for each.
| Code | X12 text | The payer is saying |
|---|---|---|
| CO-50 | These are non-covered services because this is not deemed a 'medical necessity' by the payer. | The service should not have been done for this patient under our policy. |
| CO-150 | Payer deems the information submitted does not support this level of service. | A service was warranted, but the documentation does not support the level billed. |
Many coverage policies list the diagnosis codes that support a service, and claims edits check the claim against that list. A clinically appropriate test can still deny when the diagnosis on the claim is less specific than the one the record supports.
Fix: Read the applicable policy before ordering and code the most specific diagnosis the record supports. If the indication is real but not listed, document it plainly and expect to appeal.
Policies cap how often some services are covered, such as repeat imaging, lab panels or therapy visits. A service past the cap denies as not medically necessary unless the record explains why it was needed again.
Fix: Track frequency limits for your highest-volume services by payer. When a repeat service is clinically required, send the explanation with the first claim.
Coverage policies often require specific findings, failed conservative treatment or a time period before a service is covered. A note that does not mention them reads to a reviewer as a patient who did not meet them.
Fix: Document the policy criteria in the note in the policy's own terms, for example the duration of symptoms and the treatments already tried.
An approved prior authorization does not always guarantee payment. A claim can still deny when the billed service, dates or diagnosis differ from what was approved.
Fix: Appeal with the authorization number, the approval letter and the clinical notes reviewed at the time. If the claim matches the approval, say so in the first sentence of the appeal.
Medicare covers items and services that are "reasonable and necessary for the diagnosis or treatment of an illness or injury," in CMS's words. The written criteria for specific services sit in three places.
| Policy | Who issues it and where it applies | Where to find it |
|---|---|---|
| National Coverage Determination (NCD) | CMS, through an evidence-based process with public comment. Applies to Medicare nationwide. | CMS Medicare Coverage Database |
| Local Coverage Determination (LCD) | A Medicare Administrative Contractor, defined in Section 1869(f)(2)(B) of the Social Security Act. Applies within that contractor's jurisdiction where no NCD controls. | CMS Medicare Coverage Database, filtered by your contractor |
| Commercial medical policy | Each commercial payer, for its own plans. | The payer's provider portal or published policy library |
Check the policy version. Use the policy in effect on the date of service, not today's version. Save a copy with the effective date for the appeal file.
The remark code (RARC) next to CO-50 often names the policy or the missing element. It tells you which criteria the appeal has to answer.
Find the NCD, LCD or commercial policy for the service and list its criteria. The appeal should answer each one in order.
Include the ordering note, relevant history, test results and the treatments already tried. Highlight the passages that meet each criterion.
The letter states the indication, maps the record to the policy criteria and explains why alternatives were not appropriate. Cite professional society guidelines where they support the service.
Ask in writing for a call between the treating physician and the payer's medical reviewer. See the section below for how to prepare.
For traditional Medicare, a redetermination request is due within 120 days of receiving the initial determination (42 CFR 405.942), and the next level is reconsideration by a Qualified Independent Contractor. Under federal rules for most non-grandfathered commercial plans, (45 CFR 147.136), the member has a right to external review by an independent review organization after internal appeals, and the provider can usually act as the member's authorized representative.
Opening: "I am appealing the denial of [service] for [patient] on [date of service], denied under CO-50."
Clinical summary: Two or three sentences on the condition, the history and why the service was indicated.
Policy citation: "Under [payer] policy [number], this service is covered when [criteria]. The enclosed record shows [evidence for each criterion]."
Supporting evidence: "[Professional society] guidelines recommend this service for patients with [condition] (citation)."
Peer-to-peer request: "I request a peer-to-peer review with your medical director."
A peer-to-peer review is a call between the treating physician and the payer's physician reviewer. Payers set their own rules for when it is offered and how it is requested, so check the provider manual and the denial letter.
Prepare the physician with a one-page summary: the policy criteria, the page of the record that meets each one and the clinical reason this patient needed the service. Keep the call to the criteria the reviewer applied.
A cardiology group bills a nuclear stress test with a chest pain diagnosis code. The payer's imaging policy lists covered indications, and the remit returns CO-50.
The note documents exertional chest pain, two cardiac risk factors and an abnormal resting ECG, which match the policy's covered indication. Only the general chest pain code was on the claim, so the edit failed.
The billing team appeals with the policy criterion quoted, the note and the ECG attached, and the corrected diagnosis coding. If the reviewer asks, the physician is available for peer-to-peer.
Build a policy reference for your highest-dollar services. List the covered indications, frequency limits and documentation requirements for each major payer, and update it when policies change.
Code to the specificity the record supports. A diagnosis that is less specific than the note is the most avoidable cause of a medical necessity edit.
Document the reason for the order. One sentence naming the indication, duration and prior treatment answers most policy criteria before anyone asks.
Use an ABN for Medicare when coverage is doubtful. An Advance Beneficiary Notice of Noncoverage (Form CMS-R-131), signed before the service, lets the practice bill the patient if Medicare denies the service as not reasonable and necessary.
Review high-value claims before submission. A check that the diagnosis and the note meet the payer policy costs less than an appeal. For practices with several locations, we run that check site by site as part of our billing for group practices.
We build the appeal packet with the policy criteria mapped to the record and request peer-to-peer review when the case calls for it.
Learn About Our Denial Management →CARC 50 reads "These are non-covered services because this is not deemed a 'medical necessity' by the payer." The payer decided the service did not meet its coverage criteria for this patient. The CO group code makes the amount the provider's responsibility unless the denial is overturned.
Pull the coverage policy in effect on the date of service, then show from the record how the patient met each criterion. A letter from the treating physician, supporting guidelines and a request for peer-to-peer review make up the packet. For Medicare, file the redetermination within 120 days of receiving the initial determination.
CO-50 says the service was not medically necessary at all under the payer's policy. CO-150 says the documentation does not support the level of service billed, most often an E/M level. The first needs a clinical argument, while the second needs the note mapped to the level billed.
Not with the CO group code, which assigns the amount to the provider. For Medicare, a valid ABN signed before the service lets the practice bill the patient. Commercial plans have their own rules for patient waivers, set by contract and state law.
