CO-155 denial code
Patient refused the service or procedure
How to fix it
Confirm what was actually delivered and bill only that. Where the service was delivered, appeal with documentation.
How to prevent it
Document patient refusal explicitly so partial encounters are billed accurately.
In practice
A patient arrives for an infusion, is prepared, and declines the treatment after discussing side effects. The practice bills the infusion and the claim returns CO-155.
The payer holds a record indicating the service was refused. That record may come from the patient, from an earlier claim, or from documentation the payer reviewed, and it contradicts what was billed.
Bill what actually happened rather than what was scheduled. The assessment, counselling and preparation are real services with their own codes; the infusion that did not occur is not billable regardless of the resources consumed preparing for it.
What sits behind it
The commonest cause is a claim generated from the schedule rather than from the encounter. Where charges drop automatically on appointment completion, a refused service still bills, and nobody notices until the denial arrives weeks later.
Refusal documentation protects the practice in both directions. A note recording what was offered, what was declined and what was delivered instead supports accurate billing and also evidences that the recommended care was offered, which matters for quality reporting and for liability.
Where preparation costs were substantial and the refusal came late, some payers will consider partial billing with a reduced services modifier. That depends on documentation showing what was actually performed before the refusal, which is a further reason to record the sequence.
Related codes
Terms used here — Charge Capture · Modifier · Denial
How we handle it — Medical Coding · Claims Management · Denial Management
Primary sources
The rules behind CO-155, at the bodies that publish them.
- Medicare Coverage Database (LCD/NCD) (opens in a new tab)
Centers for Medicare & Medicaid Services — Searchable national and local coverage determinations. The direct answer to whether a diagnosis supports medical necessity for a given procedure.
- Medicare Benefit Policy Manual (opens in a new tab)
Centers for Medicare & Medicaid Services — What Medicare covers and under what conditions, as distinct from how a claim is processed. The starting point for any coverage or medical necessity question.
- Advance Beneficiary Notice of Noncoverage (ABN) (opens in a new tab)
Centers for Medicare & Medicaid Services — The form and the rules for issuing it. Whether a non-covered service can be billed to the patient usually turns on whether a valid ABN was obtained beforehand.
Looking for a different code? Search all 190 CARC and RARC codes
Questions about CO-155
Usually because charges drop automatically from the schedule rather than from the encounter record. Where completing an appointment generates the charge, a service the patient declined still bills, and the discrepancy only surfaces when the denial arrives.
Yes — the assessment, counselling and any preparation actually performed are real services with their own codes. What cannot be billed is the procedure that did not happen, however much preparation preceded it.
What was offered, what the patient declined, the reason if stated, and what was delivered instead. That supports accurate billing, evidences that recommended care was offered for quality reporting, and provides the basis for any reduced-service claim.
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